Do either have a thick enough bottom end, main bearing web, connecting rod, crank journal or head sealing ability to deal with the 14 to 1 or greater compression ratio? What sort of volume does the combustion chamber have and will you need a dome piston to get the compression ratio you need? Does anyone make a sturdy enough piston with the multiple compression ring support needed for a diesel?

I recall Olds or Buick built a few pass car diesels in the late 70's early 80's using some production big block as a base, and they had reliability problems.