Not gonna lie, I don't think I have ever heard of a successful V8 swap into a 7th gen Celica. The engine bay is simply too small and the entire platform would require far too much time, fabrication, and money for most enthusiasts to consider unless you have a huge budget.
However, if you're committed, I'd say anything is possible. I have heard of a few V6 or inline 6 swaps and RWD conversions. Consider a 6 cylinder swap, it is much more achievable on a 7th gen.