Your bike is definitely one of ours and the frame was completed on 16th June 1989 - hence the frame number...
Just to clarify how we worked and named our frames: Frames bearing the "Swallow" name have only ever been as one off bespoke frames for individual customers. We always used Reynolds or Columbus tubing (we'd choose tubing to suit rider and style) quality or hand cut lugs or lugless construction plus Cinelli cast bottom bracket shells and fork crowns. Certainly while we were based in Essex 1981-91 Swallow frames were built by Peter Bird or myself. Swallow frame numbers are prefixed SW and are sequential.
Our frames with other bird names: Toucan (tandem), Giffon, Merlin, Ptarmigan, Wren, Swift, Osprey and Puffin were all what could be called semi-custom with set designs using standard tube sets, standard lugs or lugless construction, pressed steel bottom brackets, standard braze-ons (with some options at an up-charge.The frames were made to measure, rather than fully bespoke and were still made by Peter or myself, with some of the work was done by apprentices and other employees. At the time these were still very high quality frames compared to other sectors of the industry.
Fitting SA drum brakes was not an oddity as disc brakes were not available back then and the drum brake gave all weather performance, compared to basic cantilever or the useless U brakes.
Looking at the photo the bike looks all original (and in good condition) including Columbus tubing decals and the '80s smoked paint. The smoke effect was made using a candle or burning our brazing torch 'dirty' around the tubes before the final clear lacquer coat was applied.