They allow to turbo or supercharge the factory engine in 1975 and earlier vehicles without engineering so it means I had to use an a10. If I have to engineer then why not go for the E15et as I believe it to be a superior motor to the a15. I get ohc, factory turbo, turbo manifold, injection, turbo oil passages aswel as a larger valve, angled valves and factory oval ports. It also will help because I won't have to do any emission testing with factory components. I am currently designing a bracket that will allow use of the factory dizzy using a small gilmer type setup of the cam to drive the dizzy allowing the use of the factory computer. Once it's all done I will post up the how to on here. E15et motors are cheap. I bought 2 running ones for $150 each so doesn't get much cheaper then that for a factory turbo engine. Tight a$$ conversions here we come lol