Quoting BluFalcon:
You can use a 20G wheel with the E316G bearing housing and TD05 shaft without any machine work. However you will need to source a 20G compressor cover, or have the E316G comp cover machined to accept the new wheel. Of the two choices, I would go with sourcing a 20G cover, unless your trying to pull a fast one and have a stock looking turbo for anyone peeking into the engine bay. The 16G cover is way too small for the 20G wheel, and while it can work with the proper machining, it's far from ideal. Using a 20G cover however, will require you to change your intercooler piping to accommodate the new outlet on the cover.
Also once you rebuild the CHRA and install the new wheel, the CHRA will have to be balanced in some way. A shop can either balance the assembled CHRA or balance the rotating assembly out of the cartridge and index mark the comp wheel, shaft and compressor nut. The rotating assembly would then have to be reinstalled into the bearing housing, with the index marks aligned.
I bought a 20G wheel and 'evo3' style 20G compressor cover to suit, it's basically a copy of the Evo III 16G turbo (complete with correct part numbers) but the inlet snout is bigger in diameter to suit the 20G wheel. It bolts in place of the 16G housing. I got it from Kinugawa Turbo in Japan, although the parts came shipped to me from Taiwan. I purchased the genuine MHI rebuilt kit along with it, came to about US$240 all up including delivery. Got it from kando_dynamic on eBay.