Not easy to answer a question of the differences in pump performance due to the "which pump" variable. In general, Saginaw pumps run about 200psi more maximum pressure than Thompson pumps, so, depending upon which pump you are using, you could have a little less or a little more pressure. Thompson pumps run minimum of around 650psi, -meaning that a pump will function in a system at that low of a pressure- to a normal operating pressure maximum of 900-to-1,100psi. Saginaw pumps max out in the 1,000 to 1,200 range. Regardless, this isn't enough of a difference to kill your seals.
Adjusting pressure in a Thompson pump is a fairly difficult ordeal requiring pump disassembly and a lot of trial and error fiddling. Adjusting pressure on a Saginaw pump is a matter of replacing the output pressure controller in the output line. It's not simple, it's just easier than a Ford pump.
If you can, try to find papers published by Jim Shea. He was the engineer who designed the divorced PS system used on C2-C3 Corvettes and other GM cars from the early '60s through the '80s and is the identical system used on Fords Unibody cars. His knowledge base is very thorough and he no doubt has published information of the PS pump.
