I got this bike as part of a deal. The PO was sure it is a Reynolds 531 Raleigh, but it doesn't look like any Raleigh I've seen before. A US model perhaps? I'd appreciate any help that can lead to the identification of this frame. TIA.

It looks to have been repainted at some point, and it came with an incomplete set of various parts:





I don't remember ever having seen that rectangular cutout in top of the BB shell. There's one on the bottom as well. It is English-threaded.





The holes that would have held the headbadge are approximately 4.6 cm's apart:



The serial number is mostly illegible, but starts (or ends?) with an 8.



The dropouts look to be forged, but there is no brand name, and no adjuster screws either.