Battling overheating new 360 build

Any idea where to FIND an overdrive water pump pulley? I have been looking since yesterday, don't see anything offered. Looks like OEM is just shy of 6"

You don't need a different pulley. You have the correct pulley for a non a.c. 8 vane water pump.
You need an 8 vane pump like I mentioned on page 1 post #4.