Factory was on the block I believe, but the alternator bracket will work also. Another thing to remember, it a ground strap to the body also, usually the radiator core support will work. For the body systems to get grounded, this is necessary, as the engines are basically rubber mounted and usually insulated from metal to metal contact with the body. The reason the main ground should go to the block, it that the starter can draw as much as 200 amps, and needs the big cable.
Search Chevrolet Chevelle Questions
Chevrolet Chevelle Experts