'90 celica GTS

Can I turbo it w/o a engine swap?

yes u can, but itll cost u roughly the same and it wont allow u as much boost. maybe 8?

poweredbytoyota.com There is a kit there you can mock and get the parts for cheaper

3sgte turbo manifold, ct26, oil return lines, and all other parts need for the set up...roughly will cost you about $400 to $500! or better yet go with a 2.1 turbo...thats a 5sfe block with a 3sgte head...big power but ailttle more work and money...but well worth it. ask the mr2 guys in this forums...they'll point you in the right direction. good luck