Actually, I'm not trying to make a car fast. I'd like to get an early 70's Diesel that does 0-60 in less than a day...

Thinking out loud here....VStech, You mention modifying the head of a 617. Is a 617 an early 70's diesel? I'm guessing that you're talking about modifying it by enlarging the holes from the prechamber to the main chamber. And, you're concerned that that would lower the compression ratio. Could the head be shaved just a little to bring the compression ratio back into line? Would it defeat the function of the prechamber?

Surely someone has thought of this?