Ed, I got the F body bushings when I got my 36 mm swaybar. When I put them on, and tried to use the old brackets, I couldn't get them to tighten down "flush". I was afraid to just use brute force, 'cause I didn't want to strip the holes. Then I bought the F body brackets, which turn out to be the same size as the Buick brackets, with a slightly different mounting. Since the were the same size, I couldn't figure out why the bushings should fit them, but not the old brackets. So I used the old brackets, lubed the outside of the bushings, and tightened them "hand tight". They didn't tighten down flush with the frame, but the next day, I could turn the bolts another turn or two. After three or four tries, I finally got them down flush against the frame. (Each time I went to tighten the bolts, I whacked the bracket with a rubber hammer, to help the bushings seat)
I have the F body brackets, somewhere in my collection of useless parts and pieces. Anybody want them? Guess I could sell them, along with the old front and rear bars.