I'm planning on mounting the cable-x in the engine compartment. There's enough room behind the dash, but I don't want any motor "whirring" to be heard when driving along. That would ruin the ambiance of a 1974 police car.
The Feb 2012 issue of Mopar Action lists another option - the TCI speedo control unit:
I got it without a drive cable. We agreed that whenever I got it installed, they'd make me a cable that I needed. They'll probably forget about me by the time that happens, but at least there's a source for making cables of whatever you need.
your friend in screen accurate speedos even with a non-stock transmission, arthur