Ok, the Bosch is in the car and the car is running great.
Here's my how-to. There are probably easier ways to do this, but here's my way:
1. DON'T buy a bunch of fittings. I have a shelf full of expensive unused Earls fittings, and the only 2 I needed were the M12x1.5 -> male -6an, plus a -6an 90deg. There were no M12 -> -6an 90deg fittings locally, but that would work too.
2. DO buy a bunch of dremel cutting wheels. I went through a container of them as I hacked the sending unit to bits.
3. DO if possible (verification needed as to fitment) find a DSM sending unit and butcher it instead of a GVR-4 one.
This pic is a mock-up of the final fit. Notice that the sending unit cut to bits. Notice also that the fuel level unit has been removed, I took it off while I was working the dremel. More on the level unit later.
My plan was to use the fitting that came with the pump, and seal it to the underside of the sending unit. The problem is that the sending unit is not flat underneath and i tried to grind it flat to create a sealing surface, but I didn't have the tools or the skill to do it. I decided that I'd get the fitting welded to the bottom of the sending unit instead. Fuel leaks are the last thing I want to worry about.
I had to enlarge the hole in the sending unit to allow the M12x1.5 fitting to go through. I used a die grinder and went really slowly, and got the hole to be just the right size. The top of the M12 fitting happened to be nearly flush with the top of the sending unit.
This is the amount of grinding done on the sending unit. It had to be bent backward, and the hole in the vertical surface had to be greatly enlarged, in order to accommodate the diameter of the Bosch. I had to grind the top flanges of the pump bracket nearly flat with the sending unit, in order for the pos and neg terminals of the pump to rotate without interference while tightening it on the M12 fitting.
The fitting welded in place. Clocking it was important, because when the pump is tightened to the fitting the pos and neg terminals couldn't be in the wrong spot. The top of the pump is close to the bottom of the sending unit, and if the pump is clocked wrong the terminals interfere with the sealing gasket, and the pump may not be able to be installed.
The wires I used were from Radio Shack, I used them when I installed the Supra pump years ago and the wire jackets were still in good shape and were still pliable after years of immersion in E85. I cut some new wire from the same spool I used back then, and made some nice short wires. I used a spade connector for the pos terminal because there's not room between the sending unit and the terminal to install the tightening nut. I tweaked the ends of the spade to be closer together than the diameter of the terminal nut, so that when I pushed it onto the terminal it had to expand a bit and 'snap' into place with no risk if it sliding off.
The clocking of the pump and the wires on the terminals. Of note: I ground a few mm's off of the terminals' length to give more clearance and to to allow the nuts to be removed if necessary. Without this, the nuts couldn't come off and the pos one is still difficult. I also re-routed the pos wire to go behind the pump instead of in front like it shows.
I was pretty happy with everything, and then I tried to install the fuel level sender. Because I bent the sending unit back to accomodate the pump's diameter, the fuel level sender no longer lined up with its mounting brackets. I sat down with a beer and contemplated many things, and eventually decided to grind away bits of the sender to try and make it fit. The end result is in the pics. The horizontal marker lines are the -no cut- zone, where the internal wires of the unit reside. I had to bend the low fuel unit a bit to fit, and ultimately I was able to mount the unit to its original location.
Here you can see that there's clearance between the pump, the fuel level sender, and the bracket. The final routing of the wires is there, and you can seem how much of the vertical bracket had to be ground away to clearance the pump's diameter.
I also had to bend the float arm out a bit, to overcome interference with the pump
Nearly The end result! The depth of the fuel sock is nearly identical to stock, it's probably about 2mm higher. If you weren't going to use the sock you'd have to lower the pump in the bracket to maintain the stock pickup depth. Prevously I used radiator hose between the Supra pump and the bracket to combat noise, and it survived fine for years in E85. So I cut a used upper rad hose and did the same thing for the Bosch.
The pump is harder to insert into the tank than the stock one, as the diameter of the opening is barely large enough to fit this thing. Because the pump is so close to the sending unit, there isn't much wiggle room like with a pump mounted lower on the bracket. I nearly had the pump in, but there was no way to finese it into the opening becaue the fuel lever sender empty stopper was in the way. I had no choice but to cut the stopper off, and I didn't take a pic of that. So, the lever still has the full stopper but not the low level one. After the pump was installed the gas gauge didn't work (stuck on E) and I figured that I destroyed it during grinding. After going for a drive to reward myself before pulling it all apart again the fuel gauge started working, so the sender was just stuck.
The pump assembly really barely fits through the opening and requires finesse and rotation to feed it through. With only 1 hose clamp instead of 2, and perhaps some slim silicone i/c hose instead of thick radiator hose there would be a bit more wiggle room.
I thought I had a pic, but I'll have to go take one since I can't find it. I used a M12x1.5 -> -6an fitting on top of the sending unit, and then a -6an 90deg fitting to connect to the existing -6an line on the car. Unlike a DSM, there's no clearance issue between the fittings and the cover plate in the trunk. No leaks, everything works great. With no other changes, base fuel pressure went from 37.5 to 42, so I adjusted the afpr and all is well. I've got 11.9 -> 12.3 afr's again.
The pump is noiser than the Supra unit, it's more of a growl than a whine. With the car running I can't hear it unless I'm listening for it and my car is pretty quiet. Externally you can tell there's a bigger pump, but I was always listening for it so it seemed more obvious than it probably actually is.
Also, the pump came with a check valve but I didn't install it. When the pump is turned off pressure falls pretty quickly to zero. Doesn't seem to affect anything under operation, and lots of web research indicates that it will not be an issue.
Here's a comparison of the stock,Supra, and Bosch pumps.