DH you are correct with the 504, in fact it even had an universal mounting to make life easier, and many other Rotary powered products of that time came with Gnome, Le Rhone, Clerget, Bentley engines.

I was actually just reinforcing the fact that a choice of engine dates from way before the F16. The OP’s question was ‘so am I correct in thinking the F16 is the first military aircraft to have that option?’.