My normal source for NAS bolts go up to 3/8 dia and rear end mounting requires 7/16
in double shear 8 fitted AN-7 bolts arm more than enough. in single shear I would cut down a commercial grd-9 to use the bolt shank best suited for the app and just enough threads to properly tighten the nut.
In my time as a race car builder I have seen everything use to put a car together and for the most part (as Ive said) we tend to overbolt the assy. Don Long use to bolt the front axle radious rods to frame and axle with 1/4" bolts in double shear, motor plates with 5/16 at the corners, steering has most always been 3/8- but 5/16 is enough.