As I'm tearing down the 496 to get #5 sleeved, I'm also trying to eliminate the HORRENDOUS spark scatter. With the EFI timing locked out to set the base timing at the recommended 12°, it randomly jumps anywhere from 8° to 22°. Zero consistency, fully random within that range.

-The oil pump drive/gear is NOS OEM Mopar
-The bushing is brand new
-The distributor is an Edelbrock EFI unit with no advance mechanism, so no slop there.
-Distributor rotor is MSD adjustable and the tip has been aligned to the terminal at 22° BTDC for optimum alignment from 12° - 32°
-Shaft collar on the distributor set to the top of the drive gear to prevent gear climb.

It also did this with the previous MP distributor. The only solid timing I ever got was when I went to a 36-1 wheel with megasquirt. Not an option with the ProFlo4.

With the valley pan off, I can see 2 things happen: I have a few crank degrees of slop in the distributor tang to the drive, and the drive gear to the cam has a fair bit of slop too. I can eliminate the slop in the tang with a quick weld bead and file to fit, but I have easily 5° at the crank due to just the gear. Cam is a CompCams nitrided solid flat tappet unit and has less than 1000 miles on it and shows no visible wear. How much play is normal?

Finally, how much can the timing chain play into this? I can hardly imagine it can bounce much even if the chain had some slack. Lots of drag from the cam should keep it steady, and wear would be expected to be a slight retard from the original set point. I'll post a video of the slop later this morning.