Yes SP allowance remains the same - welded at two points.
re: MF- made with tubing. Interesting concepts - potentially should better resist torsional forces.
But still irrelevant for us, as only one additional attachment point is allowed.
I think 2 1x2 rectangular boxes, seam welded together to make a 2x2 would be allowed. How much can from the extra vertical - prob not much.
Probably better to take the roll bar allowances and do as much as possible with that. It could even have a bolted connection to the SFCs - at least the way I read it.

The old DC/MP SFCs are only around 1" tall and 2" wide. That's what'srusting out now in my car now. (saves weight! LOL) Taller would be better and there is room to go taller without hitting the floor or going lower for about 2/3 the distance.

IMO and from what I've observed, the early Barracuda's are relatively stiff, and mid model fastbacks probably nearly as good in that respect. So it all depends what car we're talking about. But yea, for any form of racing SFCs are an advantage. A coworking of mine would place his '67 GTX on jackstands for the week so the quarters wouldn't get wrinkled from racing every weekend. That's what happens when you lift the nose up so the front tires just come off the ground using just springs and pinion snubber (and slicks of course)
He's the one that suggested I put the SFCs in - little did I know that they would knock my car into C Prepared.
Still no real regrets.