I did a ss/fg conversion of an '88 Trek 400 I pulled from a dumpster and it has been serving me well as a commuter, distance, and general knockaround bike for a little over a year. I weigh 235 pounds, so the '84 should hold up just as well for you, assuming you're not also a Sasquatch and planning to top that off with a bunch of camping gear.

When you say 700 x 23 rims, are you measuring the outer width or is that just what the current tire size is on the wheel? Regardless, you can fit a 28mm tire on a narrow (14mm inner width) rim without any problems. Heck, I have a pair of 32mm (actually measure at 30.6mm) tires on a 14mm inner width rim (DT RR1.1) right now.
The issue is less with the rim and more with the frame clearance. On my '88 400, I can't fit anything bigger than a 28mm with SKS P-35 fenders, and it's really tight.

The XT hubs on that wheelset won't fit in the '84 400 frame due to chainstay width. The 6spd hub width was 126mm, and the XT hub is 135mm. You'll need to look for a standard road hub, which has a 130mm width. The 4mm difference will be tight, but usable.

I didn't have any luck with the rear brake on my '88 400, but I was able to get a 1991 Shimano 105sc dual pivot on the front with the recessed nut. The rear didn't have a long enough bolt to clear through the brake bridge and put a nut onto.