Looks like the early versions were a single plate while the last version was double plates.I believe the the Cooper version is a double plate configuration (wi is still down so I cannot check) As I pointed out the last version with the large alloy washers in conjunction with the Campagnolo pulleys made use of current pieces.Earlier versions used obsolete derailleur parts (to all but Jan) which were probably available very cheaply and we all know how thrifty Spence was. I used the early version on my Hurlow with a TA triple and 14-28 freewheel and changed it to a Suntour V-GT when the Spence unit was deemed to worn out to really shift effectively.I hope to rebuild this unit with newer less worn derailleur body and Sport top sprung pivot. I still feel the Suntour V-GT ($5 retail) and its later version the VX series were fantastic derailleurs . I also like the Shimano Crane and Crane GS . I think my last 4 builds have all been either Suntour or Shimano and I am pretty satisfied with them. Shimano Cranksets give you some smaller inner rings (38t>) that I have come to appreciate. Talking about Spence Wolf what did he use later as Japanese components became more popular?
on my way to NAPA this AM but still currently in
MILL VALLEY, CA USA