The link pins are 7/8" and the bolts in the bottom are 5/8", so the bottom holes need to be drilled out if you’re going to put link pins in those holes. I bought a 7/8" drill bit at TSC (I priced a 7/8" drill bit at Lowes and it is $25, and at Sears it is $22, but at TSC it is $17 for a Mibro). It is thick metal, the bracket is 1/2" thick, so the drilling is not an easy task. Fortunately, I have a drill press so I took the brackets off and drilled the holes with the drill press. I was going to drill out the bottom hole and put the pins in the bottom hole like most other people (including my brother) have done, but decided it was a little too low for my tractor, so I just drilled a new hole a couple inches above that. I can lift the mower plenty high enough now and I’ve had no problems with this setup. I just left the original pins where they were and added 2 new ones. Partly because it cost more to buy two 7/8" grade 5 bolts with lock washers and nuts then two hitch pins cost! The other reason is that the bush hog will still fit a larger tractor if need be.
I moved the pivot arm (the U shaped bracket) down to the bolt below it (and moved the other brackets going to the back of the mower to the top bolt). So, now it can swing down below the brackets. This allows it to swing farther back if you go through a ditch or something. You have to make sure your pin is not too long though, or it won’t fit between the brackets. I had trouble with it binding up the first time I tried it (the pin got caught on the bracket) and had to bend the U shaped bracket so the two ends are as close together as they can get while still allowing the top link to fit in between. I also put a spacer on one side of the U shaped bracket on the bolt that it pivots on to keep the end of the pin from hitting the bracket. I hope this helps, if I had a digital camera I would post a picture.