Are my headers cooking my PS box?

I did one thing to my Federal/TRW pump, and it made a big difference in alleviating the symptoms you are describing. I changed the power steering fluid. I used a turkey baster, and sucked out what I could from the reservoir. I then filled it and ran the engine for a couple of minutes to circulate. I repeated the process three or four times, and night and day difference.
Because of the heat source next to your steering gear, use a synthetic fluid, which will resist thinning due to temperature better. Red Line makes a great product for a reasonable price.
This might work well enough to cure the symptoms while you search for a Saginaw pump and brackets. They are a much better pump. You may want to post a Wanted to Buy ad here on FABO or look on Ebay. Saginaw pumps were used with Slantys for many years. You will want to be sure about pulley compatibility. The experts here can help you. Good luck!