80mm should be OK as far as the frame handling it...those Zaskar frames were way overbuilt (in a good strong way).
Good idea on the flat bars, if you like the width and sweep of risers, there are lots of flat bars that have similar sweep and width (Titec, Niner, Salsa, Bontrager). These are getting common since a lot of 29er riders (including me) need our hand position lower to simulate our position on a 26er.