Yes, you can use a rubber line from the FPR to the steel return line. I'm not sure what type of connection you have leaving your FPR, but the steel return line is a 5/16" nipple IIRC. So, assuming you have a 5/16" nipple leaving the return side of the regulator, you'll be fine with a single piece of hose. There should be significantly less pressure in the return hose than on the supply side. This is the reason the return is only hose clamped even on a stock car, whereas the stock supply line is a high pressure clamped hose with banjo fittings.
From the stock hard line to tank, you need an adapter fitting. The stock fitting is 14x1.5 inverted flare, so you're going to have a hard time finding a rubber line that mirrors the stock one. Most people use a 14x1.5 inverted flare to -6 AN, and convert the pump hangar.
The only reason you'd need line that exceeds a 50psi pressure rating is if you intend on running 50psi or more of fuel pressure. On the return side of the system, you shouldn't be seeing those kinds of pressures.
</font><blockquote><font class="small">Quoting GSTwithPSI:</font><hr />
For anyone trying to adapt a AN line to the stock hard line here’s how you do it. You MUST have an inverted flare adapter fitting. I got mine from RCI, but they are available other places. If you aren’t familiar with what im talking about, just know if you do not have the correct fitting, the line will leak and sh*t can catch on fire. That should be enough to deter anyone from screwing the wrong fitting on. See here for a good read on some of the incorrect fittings that are used:
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Notice the flared center inside of this fitting. I included a few shots of the progression of installation from the stock hard line to the finished product with the -6 AN line installed.
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