The stop tab on a simplex dropout is in a different place than on a Campy. Obviously moving the tab forward is easy with a file, but moving back requires a fill.
If the frame is going to be painted, I braze a piece of scrap behind the existing stop, or simply build it up with brass.
But otherwise I work cold.
JB Weld, or plastic steel isn't strong enough, plus there are adherence issues, so I drill in with a 2mm drill and set a piece of spoke in for structure, then ill with JB-W, or whatever, and file to the angle I need. If you're good, this is about a 10 minute jub, not counting curing time of the epoxy, and will last the life of the frame.
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