Originally Posted by canyoneagle

Jeff Jones in Oregon makes several highly capable mountain bikes, which are designed around old-school principles.
his SWB plus spaceframe might get you close to your target. It typically utilizes 650b (27.5) wheels.
I rode the diamond frame version of this bike for a couple of years, and can attest to its capabilities offroad.
The seating position is more upright than retro mountain bikes.
anyway, worth considering, if your budget allows.