A 100 shot would be fine with your current set up. I would run 1-15 pound bottle. 5  runs. 10 if there short. The more pressure  the better. Zex has the best plate kit I think. You can fill it at most speed shops. 3-4 bucks a pound. I would run ot bassets if you run more. Ifs its a 4 bolt and h beam rods you could run about 300 +. Dont think you want to go that route tho, you would need to make a lot of changes.  Im running a 300 on mine but the boat is completely set up for it.

It seems the big unanswered question for the exhaust manifolds is do they clear the tall valve covers?

I've always used stud girdles in my drag racing engines, I woudn't  even consider building a boat engine without one. 

What do you guys run for valve train?  Does anyone know of a set of valve covers that will clear the girdle and manifolds???