[POWERSTROKE]

I'm not a big fan of the NP4500, the Dodge diesel pickups had problems rattling off the over-drive driven gear I think it was, had a splined shaft they threaded and tightened the gear on the shaft with a thin jam nut. In a situation with a high rpm smooth running V-8 shouldn't be a problem. Don't lug the engine in over-drive.
Only NV4500 I ever drove was in a Cummins powered Ram 3500 duallie, synchros were totally out of 2 gears, very weak in a third gear, so I agree, unless you KNOW synchro's are good, replace them before installing trans.

I don't think there are different gear sets for the NV4500, like the wide ratio and close ratio gear sets for the ZF 5S-47 in my old '96 F-250, the diesel engine, 7.3L PSD got a close ratio, 460 gas got a wide ratio. For your Corvette repower I would think a close ratio would work best, less rpm drop with each shift, top gear cruising would be at 3000-3500 rpm.