Hate to revive a dead topic, but to get the 4age to fit you would need to reroute the exhaust around the steering, since it is on the other side from the 3a. You would either need all the EFI gear (wiring harnesses, computer, etc) or spend the money for a carb and custom manifold. You would want the 4age from the RWD otherwise you would need to pound in the firewall to have room for the distributor. The flywheel is larger than that on the 3a so clearance may be an issue. I have heard both ways on this, you may be able to keep the stock trans, driveline, etc IF you were to take it easy on the acceleration, and I've also heard that certain items need to be beefed up.
http://www.tercel4wd.com should have some more info and help for you.
