This one makes me laugh! I went through this in March and even wrote down my technique after screwing around for an hour or so. Crazy too, because I'd done it before!!!
First a note on Rus's comment. On the L head the upper bolts are pretty short - maybe 1.5 - 2".
Okay then, here is what I wrote down for the driver side upper bolt:
You will use the left hand to thread on the nut with washer. Face the rear of the jeep. Bend over and with the left hand, palm facing the front, use your index and middle fingers to hold the bolt in or to place it in if it isn't already inserted. The bolt goes in from the rear and the nut will be between the block and the BH.
Now, with the bolt in place, place the lock washer on the bolt (under the nut) if you are using a lock washer. You can set the nut on the block right near where the bolt comes through. You are still assuming the position as before, facing the rear of the jeep and bent over. Now with the nut in place or in your left hand between the thumb and ring finger and the index and/or the middle fingers still holding the bolt in the hole, work the nut with the thumb and ring fingers until you get it started. So you are holding the bolt in place with the index finger while working the nut with the thumb and ring or middle finger. Whatever combination of fingers works best for you.
Once you have it started thread it down as far as you can. Okay, now you are done facing the rear of the jeep and can proceed like a normal guy. Place a box end or open end wrench on the bolt with the handle sticking up in the 12:00 - 2:00 position. You will hold this wrench with your left hand. Place a gear wrench on the nut and work it with your right hand. Piece of cake! (Yeah, right!)
