134mm was the nominal length for a Campagnolo 6 speed hub. As noted, a small variation (+/- 2mm) is not going to make a big difference. However, the closer you get to the dimension across the outside of the dropout faces, the more precise you have to be in having an equal length protruding beyond the locknuts at each end, to ensure the QR locking function is not impeded.

If you have to cut an axle to length, thread on an old locknut prior to cutting. That way, after the cut is made, unthreading the locknut cleans up any damaged threads.