Go back to the factory linkage. When you say "wouldn't work with higher manifold", I'll assume that means that you converted to a 4bbl. from a 2bbl. A 4bbl. locates the throttle linkage further forward compared to a 2bbl., so you need to lengthen the kickdown rod a bit (about 1 1/2" IIRC). The 4bbl. is also wider than a 2bbl., so the rod also has to be modified where it attaches to the bellcrank at the rear of the engine in order to maintain correct alignment. Make sure you attach the linkage to the carburetor in exactly the same location as it was on the 2bbl. lever so you maintain the correct ratio of lever movement- it is quite different than later kickdown linkages.