After a few full-bore climbs, it hasn't moved. I think it's ok.
Also, the rear wheel hasn't pulled over despite EM clinging to horizontal chromed dropouts years longer than everyone else (I'd forgotten how much easier it is to get the wheel out without the acorn nut fouling on the rear mech pivot, which it so often does with vertical dropouts). I do have proper Shimano 600 internal-cam skewers.