Would have thought longer chain stays would be top of the list, longer wheelbase so the front wheel stays on the ground. Most climbers tend to have longer stems. Not sure about seat tube, would imagine further forward would be better, head tubes tend to be slacker on MTBs.
So logically >42cm chainstays, 74deg seat tube, 72deg head tube, shortish top tube?
Sounds a bit like a cyclocross frame only they have higher bottom brackets that muck things up. Perhaps an audax frame or Genesis Eq?