Re: My 390 GT build
I wouldn't go with the 750 carb, ....with what your building as stock as it is...carb formula +120% would only give you a 692 cfm, so a 650 cfm would do just fine. A stock oil pump will give you plenty of lube all trough the engine, and the intake will breathe OK. Just remember....don't expect big power from your engine in such a heavy truck. Just my thoughts,...if you want to use the 460 and dump all your money there, then go VERY cheap on the 390, because as you said it's just temporary, and you don't want to have to keep fixing or tuning the 390. That can get costly!
The edelbrock (AFB) carb is like a GM quadrajet....pull it off the intake and toss it. Go with a Holley.
JUST MY OPINION!! not law or rule of thumb....
PS. CatSkinner's carb calculator gives your engine 390, 6000rpm, 80%VE a cfm between 541 & 677. I would stick with a 650