I know on my A-body, the blower is attached with I believe 3 or 4 bolts. And by heater box are you talking about the thing under the dash or the box in the engine compartment? The one in the engine compartment is just bolts as well.
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1972 Nova 355, 4 spd, rusty but something to drive.
1972 Pro-touring Cutlass S in the works....still
You either have to remove, or significantly loosen, the fender/inner fender because one of the nuts is tucked out by the fender. Some have cut a square out of the inner fender for access and made a plate to go back over. I too want to do this but I know one thing will lead to another.
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69 Camaro therapy program, 410, M22! SOLD
68 Camaro - SOLD
67 Bel Air - Hmmm.