This is a posting I have been trying to get on the list for some hours now. Bloody email!
Although the mystery has been solved I can say that the lug cutouts, length etc. are identical with my '81 Ilkeston built 531SL frameset. The fork crown is also identical. There are minor differences in the position of the braze-ons though. Could this be, like mine, a one-off special order which originally came unpainted and unbadged?
Ottawa, ON, Canada