The '99 drive train better be mint; better still 4wd & '98 cab similarly mint/sentimental as you are looking at ton of work.
Swapping the box isn't too bad; 6 bolts to frame, 3 bolts for the fuel filler, electrical connection for the lights and 2 strong individuals can lift it off.
Swapping cabs is more challenging. Start with removing the rolled cab, but don't throw it away.
Similarly, there are 6 bolts to frame, add a cable for cab to cross member which needs to be removed. You need to disconnect throttle cable, brakes i.e. master cylinder from booster, the 3 wiring connectors, steering column and transmission (manual is more complicated than auto. I think there is also a wiring harness to transmission that needs disconnecting. You may wish to remove some "delicate" items like rad, ac condenser, hood, grill, seats, etc. Don't remove doors - you want them closed to improve integrity when you lift. Cab is ~500lbs. There are probably couple more connections I missed, that you find as cab goes up. I did initial lift with floor jacks/engine crane, while I was confirming all connections had been disconnected; then a loader & engine crane for the final lift - wide strap through open windows/blanket on door frame to further distribute load. Loader took weight, engine crane at front ensures straight up lift.
Repeat for the '98 truck.
'99 has next generation PATS so it is easiest to replace the dash to get all required wiring anyways. Get keys and move ignition/door tumblers. I don't know how much of under hood wiring is identical (knowing Ford, not much).