cooling issues

I'd thought about the pump too, but the previous engine (dead stock 318 2bbl) had an 8 blade pump as well, with the old radiator core, and had no issues cooling it, no shroud and using a 4 blade solid drive fan.

The core that's in it has more tubes per inch than the standard style. According to the radiator shop its more efficient that way. I trust them as I have used them many times over the years and had excellent results. This time is a different story.

The pump that's on it is stock, except for the cavitation plate. The only other option would be a 6 blade smaller impeller AC pump, which is not what is supposed to be on the engine with the size pulleys it has on it, which are factory correct for the larger impeller pump.

If I understand this correctly: in effect if you put in a restrictor in the thermostat housing you can slow the flow rate, without changing the pump.
In theory it sounds cheaper and faster to swap restrictors than it does pumps.