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do many of the bushed boxes go bad?is there that much of a differance to be concerned about on a street car?



I'd say no. As long as the box is clean (internally), lubed, and adjusted properly you won't know the difference. Except for the 20:1 worm gear, there aren't any new parts available for these except for bushings, bearings and gaskets. A rebuild is basically a good cleaning, assembly, and adjustment to specs. You can do this at home but the cleaning can be tough if the grease is dried out (common).
FWIW, I have a '74 Dart Sport 225 car and the gear box has the 'V8 bearing lump' on it and the box that came with my 318 '68 Barracuda doesn't have the lump. I don't think they had a different die casting for gears that would get a bearing, it was just machined differently. You can ream out a bushed housing and install a bearing if you want.