Yes, the B body 11 3/4" rotor will fit on your '74 spindle.
BUT, the b body 11 3/4" rotor is only 1" wide. The C body rotor is 1.25" wide. So if even if you get those caliper brackets to work and mount those calipers, what's going to happen when the pads wear down and you exceed the intended travel of the pistons?
It will take more than minor shimming of the caliper brackets, the bolt spacing is NOT the same on the C body brackets. You'll either have to re-drill the bracket or the spindle to make it fit an A/B/E/F/M/J spindle.
You can buy the correct 11 3/4" brackets for $100-$150. They bolt right on, no shims, no spacers, no bearing collars, they use the same calipers you already have. Is it really worth the hassle of shimming the calipers, drilling the brackets, and fabbing all of this up?
