ok, the reason he went 4a instead of 3s is cause of the motor his car came with stock which was prolly the 4afe. if he wanted to do the 3s he would have to change subframes. if his car had the 3sfe or the 5sfe he could just bolt up the 3sgte.

90-93 celica's:
gt-s,gt,gt convertible all came with either the 3sfe or the 5sfe.
ST, and base models came with either the 4afe or the 7afe.

rthe only thing different on the celica 4a/7a's is location of the power steering. as its on the intake side of the motor instead of the regular 4a spot of on the exhaust side.