I have an old fuji "special road racer" frame that had a 70mm english thread BB shell. I ran a 68mm sugino 75 BB on it for a couple of months, with the lockring barely hanging on by a thread (no pun intended). After repacking the bearings recently, the lockring gave up at the furthest point of a 25 mile ride. I had a LBS reface the shell so it's now closer to 69mm. Not perfect, but better.
Note that this will change your chainline slightly. Only 1 millimeter, really.

Oh, be sure to check the LBS' work if you go this route. The place I took mine to charged me $35 for doing little more than sanding the paint off of the edges of the BB shell. In retrospect, I have spent much more on this frame than it is worth...