I did mount an NV4500 to my existing bellhousing... but that was with my 1959 GMC 1/2 ton. I had an adapter plate cut out of 1 inch thick alluminum made locally for my 1940 gmc. It was expensive. When I called Buffalo... Steve was familiar with our bellhousings, and had that pattern. He didn't have the pattern for the NV4500.
Advance Adapter may be able to come up with something also, but I am not to thrilled with them. I got the adapter for my 59 gmc through them. 1947 through about 1967 or 8 bellhousings had an index of 4.686 inches. Later bellhousings had an index of 5.125 inches. The adapter plate was indexed for the larger 5.125 bore (there's a lip that slides into the bellhousing to center the transmission) I had to machine the lip on the adapter plate down to properly index on the smaller 4.686 bellhousing. The instructions mentioned it was for the 5.125 bellhousings only, but the sales staff didn't mention that when I ordered.
Short story Long... I am driving my 59 with the NV4500 and it is far superior to the tired sm420 that was in there when I got the truck. I still have to work out some driveline vibrations though.
