[HO455]

I thought I would add some additional information to this thread. I went this route on my Burban by obtaining an extra set of used control arms and rebuilding them. By the time I was done I had four used control arm shafts off of three trucks. The measurements I show in the photos below. All of the used ones were 3" plus or minus a 1/16". The two new Moogs (K6147) I used were at 2 15/16". The measurements are from the end of the shaft to the center of the index hole. I did this to avoid the differences in the machined areas for the seals between old and new shafts as previously discussed. (Second photo) After much measuring and double checking I milled a 3/4" index hole (and finished it off with an 5/8 drill bit just in case the rivet was taller than I expected) at 3 3/4" from the end of the shaft.
I haven't got the truck on the alignment rack yet. (Still waiting for a tie rod end). But I will post the spec's when I get them. A couple of things I noticed when doing this. One is as the lower control arm moves forward it changes how the brake hoses flex and I had to tweek the brackets on the cross member to keep the hoses from rubbing when the wheels are hard over. In addition I had to move my sway bar frame mounts forward 3/4" to keep the ends of the factory sway bar from rubbing on the airbags.
The factory index holes measured 11/16" and the Moogs were 23/32". The index rivets were 19/32" in diameter. That means with the replacement shafts there is 1/8" of slop forward and back. As both of my shafts had been knocked back and had damaged the rivets, I had to drill them out and replace them with 1/2" socket head cap screws as the OP did. The old rivet holes had to be drilled out to half inch. As I didn't machine the index holes deep enough I had to grind a 1/16" off the top of the cap screws to keep them from holding the shaft away from the saddles.