Hi Paul
I can throw a little light on your Raleigh frame. Whilst I was Gerald O'Donovan's workshop manager at Ilkeston (from 1978 to 1982) we built many specials at Geralds bidding. You are right about 531SL (SL = superlight). We built about a dozen but it wasn't very popular being a thinner gauge version of 531. The Ilkeston frames normally started with SB then a number, the SB standing for Special Bicyle. Projects such as yours would be given a straight number which Gerald would specify. I am forwarding you two new Raleigh headbadges, a brass one and a stainless steel one which were normally reserved for export models. I'm afraid I have no 531SL transfers. Hope you manage to get the bike back to its original spec.
Cheers
Mike Mullett
Reading UK