Ala #7, maybe you can machine [router like cut down] the face, of those Non replaceable dropouts
to accept a replaceable dropout ..

If you can make a jig to hold your frame under the drill press ,
as a fixed rotating tool , machine ,
and supported by the jig , say made out of plywood,
so as to move the frame smoothly under the tool.
you might get a good parallel face..

or maybe, just wing it, freehand, with a dremel tool..