To use the high back buckets you'll probably have to do like the seat on Don Keen's '69 stocker:
Like others have stated, it's probably best to just store your original seats and use aftermarket seats with the brace. The brace I have just bolts onto the cross brace and was really easy to install and adjust.
Oh, and if you can fit in the Kirkey skinny seats (15" wide) and use their mounting brackets, the seat adjusters off the original seats can be used and will fit in the original holes in the floor. You just have to drill the holes in the mounting brackets to bolt the adjusters on.