If there is enough clearance between crank arn and chain stays on the left (non-drive-side), you can try to put a 1, 1.5 or 2 mm washer between BB-shell and RH cup.
Perhaps you have to move the rear sprocket a bit outwards as well (washer under sprocket or move a hub axle washer from one side of the hub to the other and re-centre the wheel.
If the frame is steel:
Before the frame is going to be repainted, ask someone who has experience to make a bit more clearance (don't look when he's doing it, he'll use a hammer and a curved, round piece of steel) by "shaping" the RH chain stay. Easy to win a few mm extra.
If there is enough clearance between crank arn and chain stays on the left (non-drive-side), you can try to put a 1, 1.5 or 2 mm washer between BB-shell and RH cup.
Perhaps you have to move the rear sprocket a bit outwards as well (washer under sprocket or move a hub axle washer from one side of the hub to the other and re-centre the wheel.
If the frame is steel:
Before the frame is going to be repainted, ask someone who has experience to make a bit more clearance (don't look when he's doing it, he'll use a hammer and a curved, round piece of steel) by "shaping" the RH chain stay. Easy to win a few mm extra.