IMHO I'd sell the SB1, spend a few extra bucks and buy a SB2. I don't understand the fascination with putting the largest barrel on the lightest frame. The SB1 will probably stretch or fail in the long run. ALL my centerfires are on SB2 frames. I keep three extra SB2 frames, so if I buy a barrel, it is likely to fit one well. Just a cautious old SOB.
Pete