What size was the old alt vs the new one your trying to install and are your bracket upper or lower mount? I put upper mount alt brackets on my 68 Cougar (was lower alt mount with smog pump setup) and the alt is close to the block but fits. But it's a stock size part. I know some larger Powermaster and other alts fit with the lower alt mount brackets. Bad thing is they were used on GT/CJ cars and run $125+ vs $30 for the stock upper alt mount brackets. Any of the brackets bent or replaced possibly? And you have the correct size bolt spacer yes?