welcome to the forum!
are you talking about the 1998 - 2003 gen 4 body? the 1994 body panels over-all should be pretty much the same up through 1997 (gen 3). and even for the gen 4, its mostly (if entirely) just the front clip that changed (fenders, hood, buper, grill, header panel, headlights/turn signals). matter fact, i don't think the beds, cabs, and doors changed much at all from 1993 to 2011.
anyway, i wanted to mention that the front clip swap is a fairly common thing to do, and is well documented somewhere around here... that might give you some insight into possible issues with the old frame and new panels maybe
for sure, if you put on a 98+ bumper, you will need to do some fancy work to get the bumper to mount to the frame rails, maybe just weld on some newer style frame rail horns or whatever they're called
and here is something to thumb through, just front end information, but might be useful to you:
Front End Swap guide 1998-2000