Conversion from 270 to 35 Whelen should just be a rebore and rifling if I remember correctly. There is a fellow in Prescott that should be able to handle that chore. A year, not that bad of a wait, especially if he is any good.
I have an 1895 that was reworked from 30 US to 405 WCF. It handles fine, allowing me to load from blackpowder ballistics to full factory specs and all in between. In truth, I tend to only run it at blackpowder levels or a little more, not many rhinos or lions wandering around where I live.