No good unfortunately Chris, I've already tried. In my dealings with them on various other projects, I have never once mentioned DeLorean, if they asked I'd say it was for a kit car.
However the /11 variant of the BG2401 must be DeLorean specific because as soon as I gave those last two digits I got an almost instant response of 'that's off a DeLorean, we can't help you'
That sounds like an issue with the speedo head itself, rather than the angle drive / cables. I had almost an identical issue, and that was after replacing the failed angle drive and cable. On mine it would work perfectly up to around 30mph and then stick, once I got up to 40-45 the needle would ping up and then work up to around 55mph then stick again. I found a guy who specialised in speedometer repairs and sent the speedo head to him to be serviced. This was at the tail end of 2013 and I have had zero issues since. Here is the website of the guy I used here in the UK:
http://www.magnetic-speedometer-repair.com although I'm sure there will be a suitable counterpart who can service the speedo in the US.
That kind of negates the purpose, the point of the one piece cable is to to remove the extra (and unneeded) link in the chain.