erratic timing on 360

I get same results with 2 lights, plus you can hear it in the idle and see it on a vac gauge, so it is really happening. Also, there is absolutely no noise, rattling or anything coming from timing chain or fuel pump area to indicate a sloppy chain or loose cam gear or anything. Its really weird.
And yes, my measured slop does seem to be around 5 degrees.

My next step is to just go ahead and take the front end apart, but i have a sinking suspicion a fresh chain and tensioner wont make a difference. The snap back and forth between two settings just screams electrical problem, like its alternating between firing on leading and trailing edge of distributor contact or something. It can’t be crossfiring, that would show a way bigger variance than 5° and it would not idle or run as well as it does. Again, no misfire, clean plugs, no backfires. It just acts like an engine that is alternating between two timing settings that are both within acceptable parameters.