Dura Ace rear hubs had chamfers on hubs lock nuts that when you aligned with drop outs it spread them apart as you pulled wheel in allowing you to insert a wheel with a say 2 to 3 mm more width than frame spacing. So that is one way to solve a narrower frame spacing than the wheel spacing. Just buy two of them and try that. A cheap answer. I used it and it worked Charles Nighbor in hot Walnut Creek