Ok - looking at an initial "cheap" way to play with while looking for a true touring rig in the next year or so - here's a photo of the Trek Antelope. It's all stock with Suntour 3000 derailleurs/shifters (in friction mode - because the index is a pain to dial in).
Looking at the top tube specs for a '87 520 (21" would be most appropriate) vs. the '87 Antelope (54 cm seat tube). The 520 is a 55 cm top tube and my Antelope is 56 cm. The Antelope is pretty upright with the high stem.
The only problem I could see is the 48-42-28 triple. I would think you'd want a little lower gearing if loaded up. The rear is a 5 spd 14-28 freewheel.
I have some rear panniers and could try to set it up with slicks and load up the panniers to see how balanced the bike is.