I bought a used Dakota 2001 gaulge cluster for my 56 C3 pickup build. The gauge cluster will fit behind the DS of the C3 dash, to go with my 2001 Dakota chassis I'll be using as the donor. The Dakota has a manual trans but for my 56 C3 it'll have a 545RFE automatic trans. I bought the used gauge set to indicate the tranny shift position. But, is the gauge set identified to a particular VIN for the chassis it was originally in? Or will I have to get it initialized to my 2001 Dakota when I get to that part of the build? My Dak will have over 205,000 miles on it when I move the chassis under my 56 C3. I have no idea yet what miles are on the odometer of the gauge set I bought. Once I have power to the gauge panel I can figure out the miles and using a signal generator I can advance the miles on the gauge panel to match my 2001 Dakota, assuming the miles are less than on my Dakota.

I don't think the vin number security issues with the Mopar stuff started until the mid to later 2005-2010 stuff.
Its very likely the instrument cluster you bought will plug into the wire connectors in your harness.
The age of the 56 would void any mileage requirements that exist, if its titled as a 56. Beyond that, your rebuilding most of the drivetrain on the truck, I wouldn't be too concerned about mileage.

Way back in the last century when I worked at a Chrysler dealership, we changed a speedometer in a 2-3 year old still under warranty car and all the was required then was a sticker stating the original mileage, and the current mileage on the odometer with the date the change was made.

Ahh,...the simple times of the past, thanks Gene.