I have the same issue with my MSD distributor in the 511 that i had with the 408. When i rev the engine 3-4* timing comes out or retards. I fixed the SB issue by adding a crank trigger. Don't want to spend any more money right now and i think i might know why these distributors have this issue. Its not uncommon, just look it up. I believe the oil pump shaft gear is lifting when engine is rev'ed and turning as it lifts causing the timing to retard a bit. How can i stop the oil pump shaft from lifting? Thanks