Why the big bore .039" fel-pro head gasket? Why not the .021" factory type head gasket?

The steel shim head gasket is less expensive, will get you closer to a desirable compression ratio and they work well.
Leave the heads at 83cc and install the correct head gaskets.

I calculate with a .021" gasket at 4.32"gasket bore a compression ratio of 9.8:1

This is a good place to be. Factory was supposed to be 10.1:1

You can shave the heads, but anticipate the possibility of having to shave the intake face of the head and taking some material off the intake manifold (an excellent manifold FWIW). DP4B