Anything on a 30-06 case would be the easiest rebore-rechamber scenario. You’ll need at least .030” greater bore than you currently have .257” to do a rebore. The other consideration is how much meat there is on the barrel at the deepest part of the flutes.
By that math, 270win is definitely out. 280win would be excellent. 30-06 would be possible. 35 whelen *might* work provided there is enough barrel mass at muzzle and at the point of the flutes.
Just a handful of skilled smiths doing reborn work these days and I’m unsure if they could do the work with the integrated rib on the barrel or not. You’d need to call around.