[FireSale]

I have those seats in my 68 Mustang Coupe which has a really difficult floor to fit too.

You do need to add more bracing to that, you don't really have much contact area. The brackets Kirkey and others make for this seat bolt to the side of it and run from front to back about 12 inches. I would at least weld cross pieces to your brackets front and back to join them into a single unit.

You will need a back brace connected to a cross member of the roll bar behind the seat.

My seat mount is constructed from 2X3 aluminum channel and a sheet of 3/16 T6 aluminum to form an elevated platform bolted to the floor in 6 places. The seat is on Kirkey brackets bolted to this platform. I can't weld aluminum but with lock washers is seems very solid. The back brace is the one Kirkey makes. It bolts to clamps around the cross member of the cage. It's out of the car now so I can't post a pic.

Not to run on, but it's a safety thing.

EDIT: I reread your captions and edited this post. You recognize the need to strengthen the brackets.