One problem with the GMC pan is the oil pickup is in the middle of the pan. On my dragster 302 I fabricated a new pickup and placed it at the back of the pan. It took some fabrication but I used common sense and some head scratching and it wasn't difficult at all.
The military pans have a much deeper sump if the extra capacity is needed. I have a friend with one of these pans if you need it.
I eventually went to an external oil pump (BB Chrysler) driven off the front of the engine with a Gilmer belt. Works great and confuses people when they look at it.
Ron
