For compression check out Patrick's pistons and see what the deck height would be. You can take about .035 from the head maybe more. You can take some from the block deck if needed to bring the pistons closer to the top. Have your machinist check the head and block to make sure this has not already been done. Shoot for 9 to 9.5 to 1.
A reground cam would be fine study the specs of after market cams and talk with the grinder.
Although not as vintage looking 4bbl carbs work great without a lot of linkage issues. Old 2X1 manifolds are not real hard to find.
You can easily use 1.86 intake valves and 1.60 exhaust valves. I think small block Chevy valves will work. You can go bigger but I don't think a street engine needs it. Find a set of the welded stamped steel rockers they are a bit stronger. I think SBC springs work but you may have to play with spring height. Have hardened exhaust seats installed. I need to find my GMC notes. It's been a while.
3.55 rear gears would work great with your OD. That's what I run with a T-5. Your BW OD will be fun. There are some BW OD threads on here GMC too if you can search them.
I just did this google search.
302 GMC build 
