I need the round hole style so I checked the ATP Y156. It doesn't list a 383 Dart as being one of the applications for it. This is why I was wondering how the measurements posted are taken. Plus, 19.5" is still a little too long unless there is some way of mounting the cable to accommodate the extra length.
Your cable may actually need to be longer than a stock 383 dart. The Performer RPM is significantly taller than stock iron. Also you never said whether you have a B or RB engine. 440 is taller than 383.
Do you have the mopar linkage adapter on the 850 holley? Something is weird here. If the cable housing is attached to the firewall and adjusted properly at the bracket ( you do have the correct bracket?) then it should work.
