I have a first generation Dakota with a good frame but the body is pretty rough.
2wd trucks are pretty scarce here in Pennsylvania, so I'm kind of stuck with this one.
Can the 2nd gen body (cab and bed) be fitted to the older frame?
I'm sure someone has tried.

I like your user name, so lets be sure people don't thing we are each other, or in any way connected.

Lots and lots of stuff will mount on a Dakota chassis. Check the street rod section and see some of the stuff that has been put on a Dakota Chassis. I would certainly put an older cab and bed on a Dakota chassis before I would a newer cab & bed. I would suspect mounting a newer cab on an old chassis would cause a lot of problems with emissions. The vehicle needs to meet the emission standards for whichever part of the vehicle is the newest.

I'll post a couple to get you started.

The 48 Plymouth business coupe (#117) is street driven. The body shell has been put on a 90 Dakota 2wd. It runs the Dakota 3.9 V6 with the Dakota 5 speed. The car has been on the road 9 summers and has been driven over 70,000 miles on the Dakota chassis.

The project truck is a 49 Dodge and its on a 93 Dakota 4x4 chassis. It will probably be on the street by spring 2021. I'm using a 96 Dakota 318 4x4 drive train in it. Both vehicles remain fuel injected. The 49 is the 5th Dakota chassis swap I've done. Gene

Usually if the newer body is worth using the frame it's on is good too. Unles you already have a candidate in mind.

99% of the Dakotas around here are 4wd, and this is a drag project.
A lot of this is idle curiosity, but there are a lot better 2nd gen bodies out
there than 1st gen.
FWIW, I did find a nice 4 banger second gen that I need to talk the wife-god into.