Got my ALU and register modeled in VHDL. I admit I found a model for the 74181 online. But I wrote the '996 myself with a testbench. I was a little rusty on my VHDL, but it comes back fast. Vivado is a little hairy too. Took me a while to figure out that I can't start my module names with a number. But it's off and running now. Next I'll hook them up together and maybe even put a databus in there. A little address decoding and it starts to look like a system!