Your best bet is to get a Complete cummmins dodge manual drive traind and convert your truck to hydraulic clutch (87 and up) had hydraulic. You will loce the Overdrive from the NV4500.
This route will also be the least expensive as the adapters are quite expensive.
There are places that sell the mounts (
http://www.autoworldmt.com/ )
The stock power will be far beyond the 6.2 will ever be capable of modified.
The 94-98 12V have hydraulic clutch, I am not sure about the 1989-1993 12V.