Those pads, with or without shims, is about the base of all alignment for front end sheet metal. On the 3100 series, I believe the early version was a single pad, the later years went to dual pad. I could be wrong on that though. I would suggest to install your core, lay your hood latch panel up there, preferably without latch, then lay your hood on top, less hood springs. See how the gaps look at the cowl. Roughly shim as necessary to get good gaps top and bottom. Remove hood and keep building your front end. Later on, with the cowl to inner fender braces in, you can triangulate the front sheet metal and adjust the core with more finesse.
