I am strapped for cash and have access to the 6 and the boxer, they are in my possession. Friend say they have them and we're willing to give them to me. I just bought my '74 620, the head is cracked in 6 places between cylinders 2 and 3. The exhaust is white from overheating. With these signs, I'm not sure how much of the engine I can trust. I only considered the other engines cuz they were offered to me for free. I had already planned on rebuilding the one I got, if I got it. If there is a chance to salvage the stock engine, that is what I truly want. I was told it is an L18, but not certain. The U67 head is no good with all the cracks.I know where to get replacement part for the engine and had planned to rebuild it if it is not a total loss.