2wd headers tend to be longtubes, 4wd tend to be shorties. Long tubes make more power, shorties don't do as much.
Do a search for camshaft, there are a pile of threads with lots of detail. There are a couple of GM cams, a couple of comps, and a couple of lunatti that usually come up.
Looking to fully utilize the L31's performance that GM could have possibly done via OEM. It's just a street truck no need for max performance but would like to get all that i can out of the L31 intake without the marine manifold. Not saying I wont eventually go to the marine manifold later, just...
www.gmt400.com
As for oil pan, S10 forums would probably be a faster resource. I'm sure there is something that fits, be it corvette, f-body, some other OEM pan, or aftermarket.