The first thing to think about is your springs. You will probably need to take them to a machine shop to get the spring seats enlargend to handle a bigger spring; in stock form they are only rated to handle around .450 lift. I dont think it would cost too much to get the seats enlargend. I would use the xe274H cam at least. I had a 355 with the xe268h cam and vortec heads, and although it ran very well, it could have benefitted from the 274h. On a 383, a cam will operate at about 300-500 rpm lower than what it is rated to operate at. If this car is not going to need to be a mild daily driver, I would recommed using the ex284h cam in a 383 with the vortecs.This cam is testing the limits of the vortec heads as far as lift and flow goes, but the vortecs can still handle the lift of this cam. You would be looking at near 500 ft lbs of torque and 430-440hp with the 284h. If you are totally against doing the spring upgrade, in my opinion, the only other head to go with is the AFR CNC ported 195cc. They are expensive ($1250), but not compared to what you would have to do to any other unported head to get them to flow like the AFRs. With a decient cam and the AFR's, you would be looking at 500 hp and 500 ft lbs on 10:1 compression.
Here is a motor you might be interested in.