Well not sure since I don't know the stock numbers on cams or anything. But here is what I CAN tell you. Like the others said, a 500cfm is way too big. I have a 500cfs on my small block Ford with a pretty nice lumpy cam in it and that is what Edelbrock and Summit racing reccomended to me. Ever look at that Cliffords site that deal with inline 6 chevys? Or try this.
www.inliners.org. Lots of info there and what I always heard is stay with a 2 barrel carb on an inline 6 because bigger isn't always better. I learned that from the guys there at Inliners.org and somewhere else that I cannot remember at this time. Those inline 6 motors are nice and run good and strong. I have a chevy 250 block sitting in my garage but my friend never gave me the head that I had him pick me up so I have no clue what to do with it now.
Good luck!