yummy,
the BPT is the simplest bolt-on kasi B6 engine pa rin siya. same tranny bell housing bolt pattern, etc.

that said, the "ultimate" is the KL-ZE V6 engine from the JDM Eunos 500 and Millennia. 200hp 2.5L V6 pero it has a lot of room for improvement, it can go up to 700hp with a turbo. yun nga lang it's kinda large.. pero people have put it into the miata so pwede siguro sa astina...

of course pwede yung Cosmo 13B rotary engine, pero the RX7 is rear wheel drive so sobrang madugo na ang fabrication nun.