justen uses a modified JZA70 Diff in a modified St185 frame ..
He himself have said the hubs were too weak to handle the torque putting to the back wheels - and is planning on making more mods to make it closer to a supra rear end then a Gt4 one .. ( remember his is turboed- and alot more grunty than a NA 1uz, and uses a tremec GB )
The firewall needed moving back , the trans tunnel was enlarged as far as i know - and its had some serious bracing done inside and out to stop it from flexing .
You might make it easier using a w55/na 1uz , but its still a big budget project , and something you dont go half arsed into , thats for sure !
Dunno if that helps or not - but just be aware as it might look straight forward but it is not .. Talk to justen on toymods if your ultra keen , and he'll lay it to you straight , no boosheet, on what the swap involves to do it RIGHT and safely
if your still keen on 1uz RD and kinda cool - maybe look around for a GA70 - that swaps alot more straight forward , and looks much more " suiting " to a 1uz RWD platform