Almost anything built or sold by Rivendell. You might find a complete bike for less than you can buy and build an old mountain bike. My 1989 Bridgestone MB-3 checked all your boxes including eyelets for racks/fenders and it has handling that was quicker and closer to a road bike than most of its competitors of the same vintage. Plowing through deep sand/gravel I preferred my pal's Stumpjumper because its relaxed geos helped it go straight where my Bridgestone's front wheel wanted to hunt and weave. But, on pavement the MB-3 felt a lot more nimble and not twitchy at all. When I got a FS mtn. bike I replaced the stock flat bars on the MB-3 with some "Priest" bars from Riv. They are similar to their later "Albatross" bars. They worked well enough for me with the stock stem but I could have raised the bars a lot with a Nitto Dirt Drop stem or other high rise designs sold by Rivendell. I think you can find a lot of examples of this kind of bike set-up on the Riv site archives.