The 1JZ and 2JZ will not be an easy fit.
A few people have done it before to early RWD Celicas (all 3 RWD generations have similar size engine bays) and all of them said it was a pain in the butt and that they would never do it again.
The main trouble is sheer length.
Even when placed as far back in the engine bay as possible, the extra 2 cylinders have to sit ahead of the front wheels.
This absolutely kills handling and makes it a death trap on corners.
Three solutions.
1. Recess the firewall by at least 3" .
Expensive and difficult but the only correct way to keep the handling with that engien and that body.
2. Supra
The Supra was designed for the similar size 5M-GE 6 cylinder engine.
An upgrade to a 1Zj or 2JZ is dead easy and has been done many times before.
It's not hard for a worked 2JZ-GTE to give you the power you want in this chassis.
And the Supra already has IRS and an F series diff which you can upgrade to a G series diff (see caveats in previous posts).
3. 1UZ-FE
The Lexus V8 is very compact and fits into the RA64 engine bay.
Add twin turbos, a suitable cam and an aftermarket computer and it will give you the power you want.
The 1UZ-FE is so over engineered that it handles up to about 500-600HP with bolt-ons before it needs any internal work.
You will still want to upgrade the rear end.
Not quite a trivial upgrade but still within reason.
I've been doing something similar to my 1980 Toyota Carina.
http://members.iinet.net.au/~stepho/mods.htm#CarinaV8
I'll repeat what I said at the beginning - a 1JZ or 2JZ in an RA64 Celica is very hard (if done right) or a death trap (if done wrong).
- Stepho