Well, it was the timing. I set up the distributor cap/plug wires by the drawing and photo in the 77 operators manual. Off by one--had everybody skip one to the right, a sniff of starter fluid--viola! Tractor go put-put!

Compression numbers seem good (I checked while I was discovering TDC for number 1 cylinder) -- 120 to 140 for all except number 1. That one read 80 to 100, but I was doing this by myself and had my arms stretched as far as they would go to push the starter button and hold the gauge in the number 1 plug hole. Might be better, I don't know.

Thanks to everybody for all the great input and advice. Even without a muffler this baby purrs. I'm looking forward to nailing down all the details now that it looks as though she's gonna run.