I have been out of the loop for quite a few years but generally there is a penalty for modification of any emission control system on a motor vehicle. Any engine change, even for an identical one required notification. Any change in the fuel also required notification and I believe re inspection for safety. A lot of people simply did it and took their chances and few ever got caught unless they were being watched because of other nuisances the were being to the Ministry of Transport. Of course any accident that could be remotely connected with the work done, would void insurance. This is in Canada but probably pretty similar in the US.
I think more often diesels were swapped out to gas engines at least in Ford and GM trucks. Chrysler were more dependable as diesels though there are lots of loyal Ford and Gm diesel fans. Generally you can find more ready made components if you keep the swap within the same Brand. Watch the weight closely and strength of front end components if you consider the Cummins. My son had one and it pounded heck out of front suspensions.There can be lots of little details sorting out linkages for throttle and clutch, guage compatibilty, radiator and exhaust connections and the availability or lack of vacuum for brake assist on a diesel.
Resale value is about zero on anything like that.