Another thing to check is that the
oil pump drive shaft is not too long. Drop the pan, and with the dist. and
oil pump installed, make sure you can move that shaft up and down slightly. If it is too long you will crank down on the dist. adjustment bolt, but the gear teeth will not be meshed with the cam gears properly.
New
oil pumps are really cheap. If you haven't changed it, I'd do that too.