Chances are you are going to spend £300 on a frame that still wont be exactly what you want. You would be better off spending the money on a classy, modern steel frame that wont cause you any issues. Something like a surly steamroller or genesis flyer.
Filing drop-outs takes and age but will be fine. 26tpi bottom brackets do turn up, look on retrobike for that sort of stuff. Your probably best cleaning up the cups you have and maybe replace the bearings.
Chances are you are going to spend £300 on a frame that still wont be exactly what you want. You would be better off spending the money on a classy, modern steel frame that wont cause you any issues. Something like a surly steamroller or genesis flyer.
Filing drop-outs takes and age but will be fine. 26tpi bottom brackets do turn up, look on retrobike for that sort of stuff. Your probably best cleaning up the cups you have and maybe replace the bearings.