I'm Sorry... but alot of people are trying to avoid answering your real question.
These are facts... not my opinion.
A guy over on club4ag did this years ago
(http://forums.club4ag.com/zerothread?id=4179)
Standard 4age (was a bigport, but comp difference between smallport *shouldnt* make any difference).
Standard Ecu
Standard injectors
Standard airflow/map sensor
Tiny Turbo = 5-7psi boost.
He should've made atleast 100kw atw - thats better then a 20v.
This would be even more do-able with a sc12/sc14 because sc's are max 8 (standard pully) anyway, find a bigger pully and the pressure will drop (I thought of even using a powersteering pully to drop it to 4-5psi - to be safe).
I'm in the process of doing this just for proof of concept on my ae82 Bigport.
sc12/14 - $250-$350
Intercooler/Pipeing - $180
Retard the timing - $0-$50 (either you do it or a mechanic)
And maybe changing the pulley to reduce boost - $10
I've tried to do the 20v/gze conversion before... i've owned a gze before.... and its just not worth the hastle trying to swap one in (let alone converting to rwd for you).
Everything will go in no worries, but the wiring / getting it to run right is the killer.
If you get the auto electrician to do it (a good job) $1500.
The standard 4age setup is very adaptable, I'm sure you've noticed this (its why i love them so much).
In conclusion.... why spend $2000+ and 3months work to get a 4agze
when you can get the power you want with a simple bolt on setup - $500 and 2 days work.
Hope this helps.