So my take on conversion. Having rode an 89 Panasonic Mountain Cat for over. 7000 miles on 700c x 28 tires now, I like it. The geometry is almost identical to their road bikes that I find myself easily keeping up with roadies with similar capabilities, as well as making for a great commuter with a rack and panniers.
That said, if I were to do it over again, I would do 650b (27.5). I would be able to fit a x40 tire on there for gravel and/or mud guards easily. As is, if I still had the original front fork the clearance on the front would be too tight, and the rear could maybe squeeze 30, but I doubt it. Everything as far as anyone but knowledgeable cyclists is by appearance a road bike. For the foreseeable future all that won’t change. If I find a super cheap project road frame (Panasonic DX3000 or better or one of the better Fuji like a Del Rey) then will build a new road bike and turn this into a pure gravel grinder with commuting duties.