bout two days after I took delivery of my new '65 1/2 Mustang with 'K' engine, I bought a little gizmo that made the secondaries mechanical. It was a little, stamped, part and depending on where you placed the little roll-pin also supplied in the bag, you could tailor the secondaries to either come in '1 on 1' or have the primaries almost open before the other two started. I played with it and finally set it so the primaries were almost fully in use before the back two. I got mildly better highway gas mileage that way.
It cost about $1.50 and, including the roll-pin, was a bit more complex that the above baffle gizmo. Of course, that was 50 years ago. But even allowing for devaluation of the dollar...
KS