I have used the normal 1215 valley pan (like above) on a 440 w/ a pair of 915 heads that had been milled a lot (about .080"). It will crush down were it needs to be if that makes sense. Had to cut clearance notches on the intake so the end rails of the block didn't hold it up off the intake face of the heads.

It sucks your block has been milled so much already since you're going to be testing a few different manifolds. Having to mill the manifolds to fit the block/head combo will really hurt the resale once you find which one you like the best.