[buzzinhalfdozen]

Personally I would throw out the cam walk as your issue. Though it appears you found an issue with the cam gear install, the cam simply cannot walk enough in the block to change the timing 15 degrees. The thrust plate prevents it's forward movement, and eventually the lifters will stop it's rearward movement. You mentioned you were going to try another MSD box, did you? Is the dist. wiring near any other high power devices...coil, electric water pump, electric fan? It's not unusual to see a bit of timing flucuation triggering off a dist. 1-3 degrees would be considered normal. Joe