Poor idle and off-idle performance after distributor swap

AJ/FormS said

The slot is not the problem

So if I read this correctly, you are saying the old system had the same problem. Was there any part of the Old system, reused in the new system?

I assume you have checked the timing-chain slack?

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I didn't notice this issue until I removed the factory distributor to replace a shot vacuum can. I have not been able to restore stable timing through any combination of parts, old or new distributor. It appears to be degrading with time.

You breezed past the distributor drive gear, so are you saying slop in the drive gear is normal and not the cause of erratic timing? I looked in there and it is a bronze drive gear, which is odd because the car has a comp xe262 hydraulic flat-tappet, not a roller cam.