I think another reason my first epoxy granite block was so foamy was an extreme overuse of epoxy. My first block was 22.22% resin by weight, a large percentage of which was forced to the top of my mold as I vibrated the wet mixture. I did another test block today with 18.18% resin by weight and it's much better, although nowhere near perfect still. Below is a comparison of my first and second test blocks:
And a close up of the top of the second test block.
I am also currently curing a block with only 10% resin by weight, but I can already see that it's too dry. Tomorrow I will try around 12% by weight and see if that helps.
Thanks for the help so far everyone!