If you use the AA plate, you will need a 1969 and later truck bellhousing with the 5.125 bore. You could use an earlier bellhousing with the 4.686 bore and hog it out to 5.125 inches, or have the indexing ring on the adapter plate turned down on a lathe to 4.686 inches.
I have an NV4500 in my 1959 gmc, and another ready to go in my 1940. The homemade adapter for my 1940 should fit your 1940 if you wanted to dry fit the NV4500 before swapping engines.
