i think before you get carried away on idea's for engine swaps, work out your max budget. Will you be doing most of the work yourself?? if not a15 efi turbo maybe $4-5k to get manifold made, all bolted together, tuned, bigger brakes (you will need them!!) diff upgrade etc. LZ hybrid thing maybe $6-10k by the time an engine workshop puts it all together (with brakes/diff etc). CA18 might be a bit cheaper as less mucking about trying to get 2 types of engines to work together than the L and Z. If you can do most of the work yourself, you might get it done for $2-3k maybe.

Any like others have said, you cant have top end speed/handling/fuel economy/reliability/and cheap to build in the same car (as a general rule anyway)

figure out your skills and budget, then go from there

also, a datsun 1200 with 100 to 120/130 horsepower feels a lot faster than some cars with 200hp etc!!

Disclaimer: this is all from my own experiences and opinions and may not mean anything to anybody!!