The clue to me is that you found the initial timing retarded by 4 degrees, so somebody was trying to get it running right without pinging by backing the timing down.
First I would make sure you have the distributor stabbed correctly. Set no. 1 at TDC compression and make sure the rotor is pointed toward the no. cylinder (at the cap).
If not, the camshaft timing may be OFF, which can also account for you low vacuum readings. You'll have to pull the timing cover to verify that.
Could have just been a poor rebuild job as well.
The Mallory Dist was the issue with timing set at 4 ATDC.. For some reason i was getting way to much total timing. (total timing was over 40 when i set initial correctly) And harmonic balancer has not slipped. So i droped in a G.M. H.E.I. i had here, and set it up with initial at 8