The only issue with that is that the frames were changed in 98 I believe. It may take a little custom work to get the cab to fit properly. The bed and the front end (if you go with the conversion) would be an easy bolt-on though!
The 01-03 honeycomb front end is a very easy swap on the 98-2000 Rangers. New headerpanel, lights and grill. Nothing to it!
It looks like they made it longer in 98. So the body would need to be modified like you said.
A fresh facelift gave the Ranger (and B-Series) a stronger presence and a stretch in wheelbase for standard-cab trucks (from 107.9 inches to 111.5 inches) increased comfort by allowing more legroom and a greater seat-recline angle.
the cab is about the same the core support is different along with a few others parts fenders lights header panel and so on but do what plum did and make a new core support to bolt up to the comb grill and your good to go