as I posted earlier I use Fusion 360, and just recently (three week ago!) bought the Machining Extensions....so this is new to me. Fusion has a Mach4 Post that has 4th axis already. You have to modify
the post, a few keystrokes, to turn the 4th axis post feature on. To date I've used a rotary A axis only, and the post has been adequate.

Mach4 is designed to be almost identical to Fanuc 21i, so you can usually always use a Fanuc Post and produce Mach4 compliant code. Eventually when I get a fifth axis up and running I may need to do just that.