Timing Advance Sanity Check

Not once have you mentioned the rpm which the timing was measured.
You need to measure timing at the rpm listed in the FSM (x2 on the engine) to see the maximum advance.
More important is to measure the rpm at slow idle, then the next rpms listed in the FSM (x2 on the engine).
Then you'll now the advance is within the parameters for that distributor.

I've posted a few graphs illustrating this for slants.
edit: Here's one: Dizzy curve