short answer. cheaper to buy a wrx.

long answer.

depending on what you want to do, and what you can achieve yourself. I have a 99 rx and was considering doing the same.

i've decided against it because no matter how much you save doing it yourself, you will still miss out on the fruit. eg, the momo steering wheels, nice bucket seats etc.

however, if you planed to replace these items anyway, go for it.

im not an expert, but i believe any gc8 engine will mechanically fit which gives you a few years of range for sourcing an engine (damn engine must be younger than shell rule). the ECU and loom is different regardless, so spend a bit more on a sparky and get the newest, best condition engine you can.

*disclaimer, yada yada. never done this or know anywone to do a scooby conversion etc...
(please correct me if im wrong)