Hey man,
Sorry to hear about your power steering pump issues. I wish I could provide some additional input here, but I'm running a V-belt setup off the old 283, running the same crusty power steering pump (I believe Pontiac or AMC) that came with the truck. Opted not to replace it during the rest of the steering rebuild, as it seemed to be holding its own. Keeping an eye on your threads to see your resolution. Seems way too coincidental to fry 2 pumps that quickly...
This is an incredibly amateur-hour suggestion, but you are certain the pullies are all running perfectly aligned with one another? Otherwise the belt could be pulling unevenly...
The rest of the build is looking great! I'm dying to get mine back from the shop to figure out what the next project will be...