Well I finally got the 420's motor taken apart far enough to see why it would not start... passenger upper guide broken, driver upper guide beginning to come apart, timing chain still intact but quite loose, driver head appears damaged.
The head has four valves that appear collapsed as the rockers were sitting beside the valve springs!
Each valve is an exhaust side... so there was no compression on that side when trying to burn fuel. Luckily no parts fell down into the crankcase, everything was sitting up top. Is this motor an interference motor?
So, what should I do in this situation? I could get a 560 or Euro 500 motor for about $1000 to drop in there, but it would still need timing chain done almost certainly. Then on the other hand, if I rebuilt the entire top end on the 420, it would be basically new minus some wear on the bottom end. I don't see why I couldn't get 400-500K from a M116/7 with a rebuilt top end. I'd have Metric probably do the heads.
Thoughts/opinions?