I finally got the front and rear sway bars installed today. I got the Addco 550 1 1/8" for the front and the 990 7/8" for the rear. My hole pattern on the rear was similar to yours but they were farther back from where you measured yours from. My front hole was 6 3/4" back. None of the holes were threaded.
I got Addco to send me 2 of the u bolts and used them for my install. I was able to use the front hole and had to drill a new hole for the other end of the u bolt. I also took a piece 1/4" flat stock and sandwiched it between the frame and bracket for better support and to help lower the bar just a smidge to give me more clearance between the bar and the area in front of the fuel tank.
I haven't had a chance to drive the car yet but I'm for sure I will notice a big difference.
Old rear sway bar. Brackets were welded on.
View attachment 57048
Frame holes.
View attachment 57050
Rear bar installed using u bolt and 1/4" flat stock.
View attachment 57052