On the large early 2-tons they used a different system that may be adaptable to your issue. From their floor brake handle they ran two cables from the crossbar on the frame back to the brakes (interior to frame). You can source swaged cables from industrial suppliers that you could clevis on the one end at the bar and then do the same at the brakes with a similar fitting. This would be a measured fabricated cable to your exact needs. I do not believe you will have great luck with a connector between cobbled bits. The alternative would be to go to a source like speedwaymotors.com and adapt street rod e-brakes (several options) as this problem is common to those set-ups as well. An example from speedway Item #: 49108004. Good luck!