I did one similar to the 35x57. I had a 7x57 barrel bored to .338 with a 14" twist. Reamed the chamber with a 338-06 reamer up to the the old shoulder. I shoot an accurate 34-200BM or the Lee 220 gr to about 1900 fps. I could easily go faster but recoil is starting to rear its head and it handles deer with authority.
The only reason I went with 338x57 was that I had everything to build this gun but the barrel. If I had went 35 I would have to buy molds, check, sizer, dies, brass etc.
Without touching the feed rails this thing feeds slicker than a minnows lip. I did also have to buy a stock blank. A Boyd's prairie hunter. I call it a 34-57 since I like the old black powder designation. The empty case holds 57 gr of fffg. I have 34 Roberts stamped on the barrel. I'm sure there's another like it in the world but I haven't heard of it yet.
I love this gun!
Several years ago I put an F14 Adams and Bennet barrel in 7x57 on a Turkish action. Shaped the stock along the lines of a mod 70 featherweight. It was my favorite rifle until I built the 34. If I only shot jacketed it still would be.