Well I put my single GT pump in (so far the highest iv seen one support was like 560RWHP...stock lines 60# injectors, no BAP, upgraded wiring) and it DEFINATLY wasnt a direct replacement.
In short I used the SVT basket itself that I modified to prevent the pump from "draining the basket" (basket is ALMOST the same as stock...the rest of the componets like the fuel gauge will not work). The stock GT dual hat system does not work for 2 reasons.
1. the outlet on the GT pump is altered so the plastic hat is in a bind reaching from the pump to the other spout that stems for the basket. And causes a leak.
2. The stock SVT baskets spout acts as a return line allowing the pump to circulate fuel...stock GT baskets spout does not allow any gas to move through it. So with the SVT basket once I loosened everything up to prevent the leak also would not allow me to build fuel pressure.
SO what I ended up doing was cutting off the plastic hat thing and connected the fuel line DIRECTLY to the pumps outlet

. Make sure you leave that little pressure valve inline...I removed it at first and it allowed the fuel to leak back through the pump pretty fast. So with it on it helped out ALOT on initial testing, and now it now holds fuel pressure with no leakdown and has been working great

.
I know this doesnt apply much to you saleen and im not sure how your setup looks right now, but basically you just need a Y fitting and run each hose to each pump. Wiring with the Ford GT pumps is pretty easy. You have to splice female addapters onto your wires and they will plug into the GT pumps seperated + and - connections.
As far as the other stuff, im not very sure....but im almost 100% positive that you will need to upgrade to a larger fuse along with the next size up (14 gauge I hear) wiring. (I think its from the fuse box to the pump but im not sure)