74 Duster heater valve vacuum or mechanical??

Thanks for the link Ted! It hadn't occurred to me yet that I couldn't just turn the valve around the other way if the action is left vs. right :D

While the heater experts are here, can I ask a related question... my '72 Dart has a heater box with only two cables (blend door and defrost/heater door, no A/C), but the dash levers have fasteners for three separate cables (blend door, defrost/heater door, and the third one must be for a heat shutoff valve).

Does anyone know which year A-body has a mechanically operated heater shutoff valve in the hose, controlled by that third cable? The reason I ask is that I'm having trouble ordering the proper Bowden cable - they seem to only be listed by year/make/model and what I'm interested in is the length!

I'm pretty sure I have a different year heater box and possibly non- '72 levers too, although the panel in the dash looks original...No idea if this car had factory A/C or not, I got it as a stripped shell. I'm committed to the existing heater box after modifying it for big-block valve cover clearance and installing it.

So, now that we know where to get a mechanical valve (Autozone has them for $15.99, the 74827 is pull-open, correct for my cables, and the 74828 is "reverse" (pull-closed). Summit has them too: http://www.summitracing.com/parts/fss-74827

Can anyone help me pick a cable? Stock appearance/fit is not important.
thanks!