here are a couple examples of early 90s hybrids turned drop bar gravel.
the trek is my brother in law's(ignore the saddle angle) and fits 41mm. It is stable geometry and double butted TT tubes.
the Univega is my first gravel bike. Way too small for me(saddle and bars are lower in this pic that when I used it), but I used it for a couple seasons to make sure I liked riding gravel and to figure out what i wanted in a properly fitting bike.
40mm tires were mounted and there was plenty of space.
again, stable geometey(so not road) makes for fun riding.
both bikes had $200-300 in them once fully built.
I wouldn't trade my gravel bike for either of these, bow that I built it up, but the Univega was a great place to start. Can't imagine cobbling a 26er together and expecting the same result. And really can't imagine riding a 32mm tire road bike and expecting the same result.