Well, instead of answering privately, i think this is something that everyone should here. It may have been covered and thoes that have doen it can add to this thread....
First things first. Most 4age's that you'll find now-a-days are for FWD cars ie: red tops, silver and black tops. This means that right off the hop, you have a problem cuz the throttle body points to the rear of the engine. In the case of the JDM 20v engines, so does the distributor. But not to worry, the intakes can be cut and modified to point in the other direction and NO MATTER WHAT ANYONE TELLS YOU...there IS enough room to put the 20v in w/o smashing the firewall. and yes, you can swap caps/rotors with ease!!! If you have acess to a blue top or are using a 4agze, then forget all that and continue to the rest of this thread...
second, the engine is higher due to the camshafts. Now, there are ways around this... one, put a cowl hood on, make your car look like a stang. two, you can lower your engine but you still have to mod your hood some to get it to fit. three, this is where you can take your frustrations out on the car with your trusty 40 oz ball pien hammer!!!! :rolleyes:
third, your OEM flywheel won't fit. Hmmmmm, well, there have been discussions on this board on how to fix this and i found that the best one is to re-index the flywheel. (using oem tranny)
fourth, the exhaust is on the wrong side. it will have to be made to work. custom headers (as i did) may be necessary. NOTE: stock center dumps may work however, if they are too close to the starter, it will COOK IT!! Make sure you shield it. If you use custom headers, the oil bung must be swapped with your 3/4A one (its shorter and not on an angle)
fifth, fuel. I used an external pump from a 200sx turbo. cut and paste. It's that simple. Wire to the oil switch. It will be on only when there is oil pressure. IE: if there is a fire, the engine stalls, it will not continue to pump.
sixth, ECU. Couple words ---> STAND ALONE SYSTEM. if this is not in your budget, the the stock ecu will be fine. If wiring is not your strong point, then get someone to help you. It's not hard but your eyes will decieve you after about 30min of soldering and re-soldering mistakes. Everything is color coded. For example: There are 2 yellow wires going to a 20v AFM (air flow meter). One is yellow, blue stripe and the other is yellow, light blue stripe. After a while it's hard to distinguish the two not to mention the injector yellow, light blue stripe, red dot and yellow, light blue stripe, orange dot!!! See what i mean??? Fresh eyes are a good thing!!
other than that, all brackets and OEM accessories will fit. Some will have to be back spaced. Steel high pressure water pipe (industrial stuff) will suffice. Some pump pullies might need to be replaced, however your stock pulley and harmonic balancer will bolt onto the crank of the 4age. The engine sits forward more (why i don't know) but you can still get everything back in. THe rad is a little tight but it still works. If you don't like it so close, you may have to move it forward some!!! Run all you lines along the exterior of the car (outside engine compartment behind fender) and route intake tubes there too!!!
THis is all I can think of right now. I'll sleep on it and I'm sure I'll remember more.
One thing to remember in any "custom" work is that it will not be done in a weekend and that this is what I incountered and you may have a different (better) way of doing things. THere is always more than one way to skin a cat!!
EDIT:
Another thing is that i have alot of automotive connections and alot of specialized tools (mig welders and benders etc) but all this was done with the usual engine cranes and was on GRASS THE WHOLE TIME. no fancy shop with lifts etc cuz i'm poor!!!

Good luck
EDIT #2:
Elaborated on wiring problem!!!