Being a bit of a cycnic I don't think the Ebay Raleigh is an Ilkeston one: I suspect a Lightweight Unit frame - still nice though.
SBDU frames could be had with fastback stays; but only on frame smaller than 60cms and those for light use. SBDU frames with Cinelli lugs did not have fastback stays.
Raliegh had a Lightweight Unit at Nottingham (SBDU in Ilkeston) that built very nice frames and some complete bicycles (I have an LU bicycle and an SBDU frameset).
Often LU frames are mistaken for SBDU ones as the LU did build with fastback stays and in greater quantity than the SBDU. LU frames are numbered differently from SBDU ones.
The SBDU effectively disappeared in 1987 when the Ilkeston factory was closed, moved to Nottingham and became Special Products.
Raleigh still made frames for Pro teams: one of the most famous bicycles (in my opinion) being Laurent Fignon's (Systeme U) bicycles in the 1989 season and TdF.
The SBDUs palmares is impressive (for another post though). I met Gerald O'Donovan when I ordered my frame.
Hope this fills in a few gaps.
Co-founder of a V-CC section, member South Eastern Road Club and owner of - 2005 Bianchi Reparto Corse (modern), 1985 Raleigh SBDU Pro Super, 1984 Raleigh LU Corsa, 1980 Allin Stan Butler Special, 1978 Ron Cooper, 2 x very ealry Roberts (late 60s/early 70s), 1975 Bill Philbrook tourer, 1966 Raleigh Superbe Roadster 1964 Allin Stan Butler Special Belgique, 1951 Hobbs of Barbican S/C, 1950 Hobbs of Barbican S/C, 1947 Hetchins Super Special, 1908 Centaur Featherweight.