Thanks for the info. Being that I’m not conservative with my right foot, I’d agree to go with something that has a better chance of holding together for longer. How much power would I be sacrificing if I used the existing edelbrock rpm 7105 manifold that I already have available for use?
If you do decide to stay with a 390, I'd try to aim for the lightest rotating assembly pieces that you can get your hands on. A good engine builder buddy of mine says, "Once you hit the ignition switch, everything that's inside of an engine is trying to get out." That's a good way of thinking about it and the heavier parts put a lot more stress on the blocks. With that being said, I just wouldn't be comfortable with hitting 700-750 hp with a factory block. I see plenty of factory 428 blocks that are cracked in the mains just from normal usage. The aftermarket blocks add a lot of meat in the main saddles and bulkheads, which is a trouble area for factory pieces. They just weren't designed with that kind of power in mind, whereas the new stuff will take 1000 hp without thinking.
As for the Performer RPM, it kinda depends on the rest of the application. I normally make about 550 hp and 590 lb-ft with a 445, TFS heads, a Performer RPM, and a fairly mild hydraulic roller that has enough vacuum to pull about 15" on a gauge. That's a 5500 rpm engine. I think we could make 25-30 hp over that with some careful part selection, while using your Performer RPM. The RPM is actually a really good manifold, but there's a point where other manifolds begin to shine.
Also, keep in mind that the cylinder head has a big bearing on the horsepower and how much camshaft it takes to hit a specific point. We offer ported TFS heads that flow around 360 cfm with a 178cc port and then Jay has his street heads coming out that will do around that as well. When you add a high performing head into the mix, it makes it easier to hit higher goals. I'm a big TFS fan, but I have a feeling based on what I've seen from Jay's testing that I may be switching teams once they're plentiful.