The Wilderness Systems backband that I used has two adjustable straps on its upper edge that I screwed into/onto the inside of the coaming just about where the two screws were that anchored the rubber stops for the original seat back. Didn't use the single lower strap at all (though I suppose you could). I drilled holes into the side seat supports about halfway front-to-back, and anchored the backband there with stainless nuts, washers and bolts. Worked great!

It is/was a great boat. Made many of my most memorable trips in it, and it always looked good (which, as we know, is maybe even more important than being good).