Slant 6 engine ignition timing stays retarded.

If BOTH slots are at full advance and the timing is still retarded
AND, the balancer is correctly calibrated to TDC, and the cam is correctly timed;
Then
I don't see any way past having to reclock the Reluctor.
There are at least three ways to do this;
1) machine a new slot in the reluctor, or
2) move the nylon drive gear
3) move the advance cam on the driveshaft.

#2 is by far the easiest
I had to do that on my last Slanty project. My advice is to have a spare gear on hand lol.