Beer can BB shims
I used a modified beverage can shim method, simply making four tiny shims that cover the flats and bend 90 degrees over the tip of the spindle by about 1 mm, enough to hold them in place while the crank is placed into position, but not enough to block the threads. I used a drop of bearing grease to adhere them to the spindle long enough to get the crank pushed on, and tightened it up. There's still plenty of thread engagement on the fixing bolt. This gained me 3mm in "spindle length" and will suffice for this occasionally ridden vintage bike until I can acquire a 68 x 127.5mm spindle. In truth, my DIY 125.5mm spindle pushed the inner chain ring to a safe distance away from the chain stay and, as a bonus, set the chain line pretty spot on. I doubt that 127.5mm spindle will ever get ordered.