I would agree that the best thing to do would be to swap it for a d16 or a b18. How ever if you have allready spent some money on starting the rebuild process I would look into arp rod bolts and head studs, cometic or oem head gasket, a d16a6 cam, distributor, ecu, intake manifold, and resister pack to upgrade that d15 to mpfi. The cam is not needed for the mpfi swap but if you are rebuilding the motor it would be a good upgrade to put the si cam in. Also consider some slightly higher compression pistons (10:1 or 10.5:1). Or option B would be to do a cheap rebuild and build a home brew turbo kit and boost it untill it blows up and than swap a better motor in.