You can convert to 5 lug from the newer Si's but finding a suspension setup from one will be next to impossible. I would skip out on it until more time has passed for people to crash their Si's and have them end up in junkyards where people like yourself can get parts like that.

In terms of the engine swap, you would have less of a headache with everything if you just threw the K20A2 in there. Or you could just save yourself all that hassle and just turbocharge your current engine. h: