NV3500 is integral bellhousing. NV4500 would mount to a bellhousing similar to your BOP housing. The BOP has the standard Muncie GM pattern. The center hole is 4.686 inches. The sm465 has the same bolt pattern, but the center hole is 5.125 inches. AA has an adapter plate for the bellhousings that fit the sm465 to the NV4500. There is a raised lip that is indexed for the 5.125 inch center hole. With a large lathe, it is possible to turn that indexing lip down to 4.683 on the AA plate to mount a NV4500 to your BOP bellhousing. It may also be possible to mount your bellhousing to a mill and open up the center hole to 5.125 inches.
It can all be done, just takes some creativity.
X2 on the 1/4 inch plate between transmission and bellhousing for a mount.
