For starters you will need to get the fwd inlet manifold cut and shut, meaning you will need to get the end of the manifold with the throttle body on it cut off and moving it to the other end, so the throttle body points it the right direction for a rwd application (dont worry about the large breather pipe in the middle of the manifold linking to the cam cover as this can be blanked off) your local engineer should be able to do this work for you - while this is happening its also a good idea to get the bracket which holds the throttle cable moved to the other side as well, some thought should also be given to how a return srping for the throttle is to be used
Next up is sorting the gear box out, you will have to remove both flywheels for starters to get the backing plates changed over so make sure you have a torque wrench for put the 4AGE flywheel back on before you start work, you will need to use the backing plate off your old 3A-U, with a 4AGE flywheel, a 3A-U clutch and a 4AGE pressure plate, it was found the thrust bearing was too short to engage the clutch, so i had to get an engineer to make up a 5mm spacer to sit behind the bearing so that it could engage the clutch, also don't forget to buy a new spigot bearing for the input shaft.
The next problem that was found was that the 4AGE flywheel was hard pressed against a part of the bellhousing and the engine wouldn't turn over, there is a bulge just under the starter that needs to be ground flat, we used an angle grinder with a grinding disc, there was also quite a bit of meat left behind even after the grinding
It was discovered that the 3A-U starter motor didn't have the grunt for turning over the larger 4AGE, so make sure you have a 4AGE starter.
You will also need a 4AGE RWD exhaust manifold, or you can buy a set of COBY extractors for about $150 which seems to be a good deal.
Use the engine mounts of the 3A-U which bolt straight up to the 4AGE, just make sure you have spare bolts as the 3A-U uses a number of studs in the block with only nuts on the end and you will run short when changing the mounts over. Make sure you have all the 4AGE ancilleries such as alternator and A/C compressor as these can't be changed over from the 3A-U
The next big mission is the waterpiping, all that was done here was shorten the two metal pipes that come out of the water pump, all that was then done was to cut down various lengths of the 4AGE and 3A-U water pipes to hook the waterpipes up to the radiator and thermstat, the thermostat was mounted on the inlet side of the engine.
The standard radiator can be used but you will need to get an electric fan and mount it securely to the radiator and wire it up.
You will also need an inline fuel pump, its a good idea to use all new line and a new fuel filter.
Slap everything together and you will find that you need a longer throttle cable, an AE86 throttle cable will do the job nicely, otherwise you will need to lengthen the existing one by a decent amount.
Now its time for the hard stuff, the wiring, make sure you have a 4AGE loom and computer, and its also a good idea to make friend with an auto electrician.
If your lucky/unlucky enough to have power steering you will need to get the lines lengthened and a 4AGE pulley wheel for the powersteering pump, and a bracket engineered to sit the pump on the other side of the engine, its a bitch of a job, try to get a non-ps steering rack, or even a non-ps AE85 for that matter.
I think i have covered everything, and if you have any questions you can email me at [email protected]