I have read of conversions to the 7.62x59 Mosin round, but it is up there in pressure tool. I concur with staying away from the 06 and 308 chamberings as well. You would also have trouble with the bolt face. The rimless cases are .473" case head and the 303 is about .540" I believe.
Personally, I would go back with the 303 chambering. Just remember that .303 is .311" bullet diameter and 30-30 is .308 bullet diameter.
I have to ask why you're rebarreling? Is the existing barrel in bad shape? Are you looking for more power or a chambering you already load for? Just curious.