Don't most of the vendors carry replacement speed-o cables? I bought one for my 67 a couple of years ago (I think it's a Ford part, not a repro). Then I went to a T5 and had to switch it out. On the length, I think they are just selling the longer one now, but that might be wrong.
In any event, I have an almost new cable in my garage that came off the 67. Let me know if you want it: I'd consider letting it go for cheap for a VMF Pooh-Bah (like for the cost of shipping!). Think of it as helping to reduce the clutter in my garage!