First time posting to any tractor forum: I greatly appreciate everyone's response. Most of them were quite helpful.
I really like teddy52food's suggestion of pressurizing each cylinder and checking for leaks.
I'll look for a 1/4" quick-release to spark-plug thread adapter later today: I assume that's the most effective way to pressurize cylinders.
Additional background: a) no - the tractor does not start
b) compression checked with all plugs removed
I'll post my findings in the next week or so: thanks again!