I finally gave in trying to make the stock replacement cable work smoothly. Nothing I tried made me comfortable with it so I removed the spring and guide. I then cut about 2.5 inches off the end of the cable that slides inside the spring guide. Reattached the threaded end by welding and used a separate return spring. Adjusted idle and full throttle stops at the pedal. The full stop bolt had been removed . It's a wonder the cable never snapped.
I suspect that part of the problem getting the original cable to work correctly was due to the carb. / manifold combination. It's why the old cable had knots tied in it. Something I noted that was poor was that the threaded end of the cable that was attached to the part that moves inside the spring guide was attached with a 4/40 threaded stud of soft mush metal. The welded attach is infinently stronger. Only need to play with return spring rates. Still not happy with the cable bracket. The cable should be firmly clamped at that point. I now have the metal to fab a better bracket. Fuel line and filter is still bugging me. Did Panteras not have a fuel filter ?