This is a neat discussion. I'd say this first, 500 shouldn't be hard to hit IMHO. I am not sure why Jay's old magazine builds fought that number, but as Scott said, that's 1.12 hp per cid. Not unreasonable, even in a tight spaced wedge like an FE, but with the cylinder head as picked, as posted, it makes it harder
That's why I think what continues to be missing here is real cylinder head discussion. Edels are decent for a cost effective build, but on the street I like to consider 2.0 X intake flow as the max a tight bore spacing wedge like an FE will pull. That's if everything is well matched. With a 260 cfm head, it's tough to be in the low 500s unless it's matched perfectlyl. That's a probably conservative number as some people can show 2.2 or so per intake cfm, but that's really more in the canted valve range or dyno only IMHO.
I still think less focus should be on a specific degree or two of a lobe, same with compression, and get that thing breathing. Just as an example a small runner, like the TFS, or Blair's small runner pro-port, would add a significant amount of cylinder fill, both normal atmospheric and during overlap. A better set of heads will do more than a 1/4 point of compression or a 3-4 degree change in a lobe. Get a 300 cfm small fast port and match parts and the 500 is far easier IMHO.
Needless to say, the quality of your offset carb spacers will also affect that. Not too worried about adding plenum on a 445 inch motor with early cam timing and a properly sized port, but, if those spacers add some sort of goofy turbulence or force the mixture to make corners it doesn't want to, it won't be as happy
That being said, I agree with Brent and Barry 100%. Stay at or under 10-ish SCR, don't push the limits of DCR (which just means cam appropriately), and the RPM range and power level is perfect for a custom hydraulic roller, especially if you can get a better flowing head on there.
I'd also remind that Barry made some good power with an off the shelf cam he didn't expect to use, not that I recommend that here, but I'd push hard to convince you and everyone else that "the right heads make real power" and the other stuff supports the airflow.
WAY oversimplified of course, but the fast guys do head work, car show guys do big cams.
As far as the gear ratio discussion, going back, 2.75 X 3.50 = 9.625, I have no idea what you were doing with your "uptick" I assume it was to account for converter slippage, but don't do that. At low torque cruise a converter will not be slipping. The stall speed is for a given torque and resistance, and a higher stall converter won't be slipping at cruise because you have neither high torque required or high resistance. I don't mind the 2.75 gear, puts it in the right place, but still make sure you have a quality converter company look at what you have for dyno results and make sure it matches. Too tight or too loose are a bitch on the street
One last comment on the nitrous, "a 2 second shot at most" is more worrisome than saying you will stand on it IMHO. Build the engine to the desired use. If you want nitrous at that level, spark retard and dedicated fuel supply is a minimum in my opinion, and having it set up as a 2 stage would be preferred as it would come on easier than just jamming it all in there. That being said, it's all about risk vs reward, if you want to take the risk, do it man, just do everything. Build it the best you can to hold 700 hp, if the block splits, it splits. I personally would want an aftermarket block for that, but it may last for a long time. Just don't think that you'll manage the engine;s internal safety while holding the button, a lot will be going on when 700 hp starts eating up pavement
