I really hate to tell a story where the undersigned comes off looking like a complete fool, but in the event that this tale may save some other poor soul the expense and embarrassment I suffered, here it is:
Apparently Jeep changed oil filter mount specifications in mid-model year in 1987, and I was lucky enough to acquire one of the ones so equipped. For anyone observant enough to see it, they put a big yellow placard just in front of the radiator on the left hand side, advising that this AMC 360 requires a 20mm x 1.5 metric threaded oil filter.
Thanks to all who addressed my question and offered suggestions--it has been a learning experience.