I have decided to modernize my Falcon San Remo - however, I have measured the rear dropouts and it seems to be 120mm. I am a little nervous about spreading the frame for modern hubs - it seems a long way to spread.

Is there a best way to spread this? I have read Sheldon's article, and looked at the Park website, but they are talking about spreading the frame by 4mm - I am looking at 10. That seems a looooong way to spread. Should I attempt this myself, should I take it to someone?

Guide me, here.