I was wondering if an 85 celica 3s-gte engine will fit in a 91 toyota with a 5sfe engine.

Anything can be done but it is not a direct swap, you probably go to some Toyota website forums and do more research. I would think the wire harness, computer, trans all need to be swapped, not sure if the axles will fall into place either, sorry, I am a Honda guy and don't have any Toy sites to play with.

It all or nothing, I am sure.