How well does the 4500 hold up behind the 4-53T? The reason I decided on the 5600 is the extra gear and the higher rating over the 4500, don't know it off hand but I know it is higher for the 5600, although if it holds up well I'd be willing to adjust the setupMy understanding is that the NV5600 bellhousing is integrated into the transmission body, and cannot be easily removed. it is true the bellhousing bolting mounts up to a 5.9L, but I do not know of a 5.9L bellhousing to a SAE round adapter(assuming your engine has a round SAE housing). I have a 4-53T with a SAE2 housing running a QuickDraw Brand SAE2 to NV4500 adapter since I cannot get the NV5600 to bolt up without making some unique transmission housing. The NV4500 has a 4 bolt pattern to hold the trans body to the bellhousing itself, that is not the case with the NV5600 per my understanding, but I could be wrong.
you can put the NV5600 input shaft in a NV4500 transmission if you wish, but unless you are doing crazy things the NV4500 1 1/8" input shaft works. Char1355 is right you need to do some unique work with the flywheel to fit both a clutch to fit the 10 spline 1 1/8"(or 1 1/4) input shaft and pilot bearing. I am having my SAE 2 flywheel machined to bolt up a stock dodge clutch but havent worked out the pilot bearing yet.