Any competent gunsmith with a 300 savage reamer can do that, all your doing is shortening the over all length of your chamber so you can crib the 300 reamer a bit deeper to get past the 308 dimensions. You loose maybe 1/2" of of threads and the somith simply re threads it deeper. I don't explain things very well mate but i'm sure oldgunsmith or gunplumber, one of the boys here can do a much better job.
John
