You're right I was thinking backwards. that would tend to put your chainline 6mm outward of the crank, but you are saying the crank is too far out.

straightening the frame is not a simple job, but it shouldn't require welding, but don't get too worried about it. Chances are this is a simple matter of getting the correct length of bottom bracket for the crank you have. you never did say what crank it is. That makes a difference. Sheldon Brown to the rescue once again. he has a database of cranks & bb lengths. Go there find your crank. It will tell you the bb, and chainline it weas designed for. then subtract to get the bb length you need for 42mm chainline. http://www.sheldonbrown.com/bbsize.html From looking at this page I can see most doubles are designed for 43.5mm chainline, and most triples 47-50mm and doubles are measured halfway between the rings if that is the case you should be able to get pretty close to 42 using the stock bb, and the inner ring. If you want to use te outer ring you need a slightly shorter BB than stock. In your case though I don't know if you have the stock BB length or not. I beleive you said you got a 110, so a 103 should get you there. cranks designed for 103 bottom brackets are unusual, but they are out there.