If the block was zero decked for the 6pk piston it's only had maybe .025 taken off, that's not too much. As long as the heads were milled on the intake face to match was was taken off the heads he should be pretty close. You aren't going to be able to use the .030 gaskets that come with that valley pan and the fel pro gaskets suck anyway , I don't know what material they are made of but they seem to wick oil?? Get superformance gaskets , I think you can get them as thin as .010 , but you'll have to egg the intake bolt holes with all those gaskets and the block deck possibly ???

If the china walls weren't cut when the block was decked then you might have an issue trying to used a solid valley plate, especially one that would go under the edge of the head.