Dump the straight antifreeze, it may have worked before on other stuff that wasn't putting as much heat into the coolant, (maybe blocks with less rust inside too, that weren't .060 over) but its thicker and doesnt dissipate heat the same. In fact I noticed my car runs 10-20 degrees cooler with straight water vs 50/50.

The fan mounting plate, as mentioned, might be an issue.

I would try a stock water pump and water pump housing if you have one and the fans/mounting plate don't make a difference.

More timing will help, some engines really run hot when you disconnect or don't run vacuum advance. I would expect that knocking it back to 28 made your problem worse.