Adjustable rockers???? If so did you adjust them properly. With the lifter on the base circle of the cam make sure that the lifter cup is at the top of the travel with the lifter, cam, push rod and rocker just making contact. Now adjust 1-2 turns more. Make sure not to adjust the 0 + off the plunger that is in the bottom of its travel.1.63 is pretty low installed height for a big block. Installed height for a big block is usually in the mid 1.83.1.86 range.