It is made from 3/8 alum. plate and uses 7/16 flathead bolts to mount the plate to the manifold, then a set of holes are drilled back 2.250 inches from the stock locating holes to move the supercharger back sealing the front of the blower up on the manifold and helping the distribution of the discharge from the supercharger to be more centrally located in the manifold.
Also the plate has been O-ringed and includes a set of cut down blower studs. To measure which plate you need measure from the center of the left most forward bolt hole on the blower snout side of the supercharger case to the end of the case.
The measurement on the blower case should be 2.625" to use this set back plate.