Hi Sal (and Hi Lisa!), other than my four-hour-a-day commute, I've been here makin' it happen.
500 horsepower is easy. The Scat cast steel cranks are a great way to get inexpensive cubes. There really isn't any alternative at anywhere near that price. To get to the big cubes, we use our aluminum block. To get a 428 block suitable for overboring more than usual, you have to go through so many blocks to get one with thick enough walls, that it's (for some people) a big hassle.
The Shelby intake already comes machined for the original "puke tank," (though some pics show it unmachined) but it can't be machined for an original style
oil fill: the runner and water neck are in the way. You could machine it anyway and install a fake one, though!
My thoughts? Depends on what you're using it for. If, like most people, you're going to run it on the street and the occasional track event, then if it were me and I were looking for max power, I'd use a hydraulic roller cam and around 10.5:1 CR. I'd keep the cam small enough that we wouldn't need to go too nuts on the valvespring pressures or the rest of the valvetrain. As long as everything was good for 6,200 rpm or a little beyond, I'd be happy.
A flat tappet cam can work very well too, of course, and is a few to several hundred dollars cheaper. We use both solid and hydraulic (mostly hydro), with grinds having duration starting at the mid-240-something degrees intake, mid-250 exhaust. I'd use something a bit bigger for a big-inch motor.
Valve size is an interesting deal. I think you were talking about using the Edelbrocks in our last email convo; I think you can run a pretty high lift cam with those without hitting a 4.130-4.180" bore but I wouldn't know, as we haven't used Edelbrocks yet and the Shelby cylinder head valve spacing is wider, and the diameters are larger (2.25" and 1.75").
What kind of rear end was in the side oiler you dynoed the other day? IRS or solid axle? The IRS'es sap a lot of power over the straight axle ones. Some folks out there have made over 600 to the wheels on IRS though!
Thanks and talk to ya soon,
Chris Weisberg
Carroll Shelby Enterprises
(310) 538-2914
Edit: And yes, since we're all civilized people, I'm talking about Dynojet rwhp #'s, as I know you are too.