Update on this. Finally got my engine block back after machining. The machinist didn't think a torque plate would be needed or beneficial, but since I was paying for it to be done that way and I was providing the torque plate, he was more than happy to do it.
In his words: "I never would've believed it. You were totally right."
The cylinders are out of round by about 0.001" without the torque plate, but become perfectly round with it torqued down using the same fasteners I'll be using with the heads. He also confirmed that the aluminum torque plate from CCA Racing is of excellent quality. He works with many race engines where he uses torque plates regularly, and this one is right up there in quality. The only issue is that the bolt holes are too small to accommodate ARP head studs. The threaded portion fits fine, but the smooth shank is too big. He had to hone out the bolt holes to make them fit.
Keep in mind that this much benefit from a torque plate might be unique to 557 blocks like I'm working with, which is a weak casting to begin with. I don't know that there would be that much change with a 988 block or something else with more substantial main webs. I've been checking tolerances as I assemble the engine, and all the clearances are spot on so far, so the machinist did REAL good
