I've owned several Stevens Tip-up pistols, including the Model 35, and have one now. So far as I am aware, they were never made in any caliber larger than .25 rimfire, and no centerfire calibers at all. There were larger, older, Stevens models made in centerfire calibers. The locking mechanism is not at all strong, and most of the Model 35's found today are loose due to wear, and that's from continued use with the original rimfire ammunition. Additionally, the frames appear to be cast iron, rather than milled steel. In summary, I do not believe the Model 35 is a good candidate for conversion to any centerfire caliber.
PRD1 - mhb - MIke