This layout looks really good, but I'm looking to build it in a 2-in, 1-out configuration (a bit strange, I know!)
I assume all that needs to be done is to add another input buffer. I copied the schematic from the linked thread and did just that, while changing the dual op-amp IC to a quad. Other than that, it is (read: should be) the same as the original. Here's the schematic: