I just stripped a rusted Jaguar XKE for it's wire and also a midget. I have almost all colors needed save the yellow black in case you need any correct wire.
Suppliers of model A parts offer looms in various diameters. Not correct for the rubberized coatings of WM20s but my 741 and XA have it and it looks okay, better than electrical tape. Just wanted to confirm its outside diameter on the BSA.