Mate, what do the Dart blocks cost over there? They're out of control over here - beautiful piece, but many guys over here end up using an early 351W block rather than spend the big bucks for a Dart or SVO block. Is there anything to stop you from going with the taller deck height of the 351W?
I've always liked the liquid filled Pro Comp gauges. The liquid really stops the nedle from fluttering. My current gauge is for EFI (100psi), and it's a dry gauge. It shakes from 40 to 45 psi while cruising, and annoys the hell out of me. When the pressure goes up with boost, it steadys. My datalogging shows that the fuel pressure remains steady, and it's just the gauge shaking around. That's not to say a liquid filled gauge wouldn't look a bit out of place in your car though....
There's a guy here in Brisbane that's regularly building 600+hp single carb motors that run 98 octane on the street, so 500 should be easily achieved with your combo. I've found that Comp Cams seem to be the current manufacturer of choice amongst the hipo ford guys here lately.
Good luck with it all,
Craig