Due to the inclined nature of the engines in 240s, more transplants are feasible. My vague memories are of Ford inline 6 cylinders from base Mustangs installed in 544s and 122s. The right 250 six with a four speed is feasible, I think, but maybe no one else alive can remember how. There were a bunch done somewhere in Montreal in 68-72 or so. I knew a couple of rich kids from Montreal who had 120+ mph Volvo conversions, but that was back in the dark ages. The drive trains were from Mustangs. Check the junk yards and the nursing homes for parts and experience.