[AndrewJ]

Yeah, an engine from the CRX HF would be best, but if you want to keep the one you have, go down the list and toss/keep all those parts.

If you get a HF motor, it'll very likely be used, and you'd probably want to do a rebuild, new gaskets, inspect all the bearings, seals. New timing belt, plugs, etc...

The alternator underdrive pulley is better than the "stock" pulley, but inferior to removing the alternator belt entirely. It depends on how far you want to go.

EDIT:
Oh, and remember, if you get a HF motor, get the HF transmission too. The motor will be next to useless without the transmission.