I too am in the process of fitting a front brake rod to my '43 M20 and need to fabricate a short brake cable from the lever to the rod end. I would certainly like for an experienced person to step up and provide the correct cable dimensions.
In the meantime, I have an old document that lists several front brake cable lengths as follows:
I grouped the associated lengths assuming the one digit difference in part number made the outer and inner cable pair.
For the brake rod ass'y, I think the 66-8737/8 is the cable pair to examine for fit. The others are way too long.
Although I have yet to fit the rod to the wheel and right fork, my preliminary measurement for the inner cable length is about 19-3/4" for a 17-1/2 inch length outer cable.
I plan to make up a custom cable from a venhill.com (also venhillusa.com) clutch cable kit with the 10 mm X 10 mm barrel and small trumpet end. I don't have a precise inner cable length yet until I fit the rod, but can publish it next week when all the parts come in.
In the meantime, maybe a more experienced reader will chime in a provide the data.
