Ok wasn't sure about that. I guess there is some type of speedo gearbox which also shifts when the rear end is shifted.
Advanced Adapter makes an adapter plate that will work with a little bit of machining. The macining involved has to do with the "indexing" or centering of the plate to the bellhousing. The bellhousing for your chevy has a center hole that is 4.686 inches in diameter. The adapter plate is made for a 67 and later bellhousing which has a center hole of 5.125 inches. To bolt the adapter plate to the bellhousing, either the bellhousing needs to be bored out to 5.125 inches, or the adapter plate needs to have the indexing lip turned down to 4.686 inches.
The NV4500 is a stout transmission weighing in at 200 lbs. you will have to fabricate a new rear crossmember to support the tail section of the transmission.
When installed the shift tower will be moved back about 6 1/2 inches from the location of the stock sm420. The shifter will be closer to the seat.
Dodge used a heavy duty and standard duty version of the transmission. The standard duty uses a 10 spline 1 1/8 pilot shaft. The heavy duty uses a 10 spline 1 1/4 pilot shaft. I know the 1/2 tons through 1 ton gm vintage trucks used a 1 1/8 10 spline clutch, however I am not sure of what the 2 ton trucks used. In my application I was able to use most of the stock clutch assembly. I had to order a speacial pilot bearing. I was able to use the stock clutch, pressure plate and throwout bearing.
The snout of the bearing dodge standard duty bearing retainer had to be turned down on a lathe to fit the stock throwout bearing. I believe there is an aftermarket throwout bearing which will work as is. I wanted to use as many of the stock parts as possible to make finding the necessary parts easier.
OK enough about the NV4500, have you searched for a "Clark" 5 speed with overdrive? This transmission was an option for your truck and will bolt directly in. The OD ratio is not as high as the NV4500.
