On the 383's that have come from other shops where they have used 2 bolt caps there has always been a problem of the caps walking in the registers and its not the HP that does it its extra stroke.
We have one in the shop right now where the engine builder told him a 2 bolt would be fine and after a couple of months running the oil pressure has been droping and they took it apart to find thatt the caps were walking and the bearing down to copper.
Here is a link to look over http://ls1tech.com/forums/showthread.php?t=652566
Hpefully they have taken care of the problem thay have been have with the Sir rods not holding there size on the big engine.
On any of the blocks we machine for a 383 and we use a good 4 bolt cap block if its got 2482 on the center caps if not we install a set of billet 4 bolt repalcement caps, we sonic test the cylinders which is a must clean and mag, line bore if new caps are installed and line hone, deck, bore and plate hone, stroker clearance the bottom of the cylinders and install a set of performance cam bearings and a set of freeze plugs for 595.00 if no caps are installed.
Here is a link to a 383 we bilt for a customer and using a good set of well prepared Vortec heads we have seen the same results on the dyno and with theis much torque and HP I know that a bolt would not live in this build.
Good luck with your build