My measurements on C Comet and B Rapide are -
Comet/Rapide UFM seat pivot (top tube) width = 5" >relates to
a dim
Comet/Rapide width of outside of the rear plates = 10½" > relates to
b dim
Comet seat pivot to swing arm pivot = 14"
Rapide seat pivot to swing arm pivot = 15¾"
My "minds gears" are slowly turning, possibly at the wrong ratio, but moving none the less.
I do not want to modify a perfect D rear section, if possible.
So if the Vincent D closed used the swing arm pivot for the bottom attach, this means the top pivot (for a D closed rear section) must reside higher, on a twin Vincent than the C seat pivot???
So I am picturing , for the Comet, fabbing a bracket like I showed below, raising D section pivot 1" or so .
Bracket narrowed to use the lower two UFM tubes, as they are narrower 4", rather than seat tube which is 5".
At the bottom Comet side plates, below the swing arm pivot fabbing some 1/2 " studs reinforced with 1/4" plate.
What about that stupid idea?