I've ordered up the nuts and bolts last night. I'm going to use a pair of 5/16"-18 bolts which will be tapped 1.25" deep into each "B" axle. I figured if I went with just one bolt in the center the thing would want to rotate with the tube where two bolts in each end would hold everything in place. Looking at 3/8" bolts they look like they'd be just a bit too big for the 2" axle.

For the lights I bought some 4.25" long 1/2"-20 bolts as the stock KC bolts aren't going to be long enough to drop down thru the 2.25" tube. Matching plastic insert locking nuts will hold those bolts in place.

I went with grade 8 bolts as they weren't that more expensive than the lessor quality ones.