The guys over at Rat Rod Bikes sent me your way to get some help with this ID. I'm fairly sure it's a bike-boom-era ten-speed, based on the rest of the bikes I got from the same storage unit. I already broke even on the group of bikes so I'm considering this a freebie. Any help in figuring it out is definitely appreciated.
The serial number is X33478 at 6 o'clock on the underside of the BB. The only component on the frame is the driver side bottom bracket cup which says "T.D.C Made in England". By my measurements the BB shell is about 70mm which I'm fairly sure is an Italian-only size. The rear spacing is 127mm. It has what looks like an integrated track for a cable attached to the top driver side of the BB, a guide on the right rear dropout, and some hooks for a frame-mount air pump on the down tube. The rivet holes for the head badge are vertically spaced about 60mm apart. Frame size is 54cm. It's worth noting that the huge rust is due to someone sandblasting it and letting it sit, so there are no paint/decals to go by.