http://i89.photobucket.com/albums/k234/Claremontcat/IMG_0503_zps75e94699.jpg

May have another part of puzzle: truck is 53 GMC - looked at service manual for
GMC 228 engine, and the distributor looks like the one on my chevy engine.
So looks like whoever did the engine swap used the GMC distributor. The Chevy
manual doesn't have a photo or drawing of vacc advance so I'm guessing they're
different