Maybe I can add a nugget of info here, something I have not seen in the thread.
I installed the EZ-Flex kit on my tandem 3500 lb axles. The trailer is completely up on jack stands because I had over/under kits to put on as well. I made sure to install with the shackles angling up from the equalizer. But after finishing, and moving on to work on the axles, bearings, etc., they drooped into the down angle positions. This had me worried a bit so I called Dexter to make sure everything was okay, that I had the correct parts, etc.
The guy said this is not unusual when the weight is off. He said when I get the tires back on and the trailer back on the ground, both springs (on each side) might just cooperate and go back into position. If not, at least one spring on each side should. In that case, put a jack under the end of the axle that is in the correct position, and jack up on it. That will move the equalizer enough that the other spring will snap up into the correct orientation.
Also, I will add an "X2" to whomever posted that it helped to spray the old bolts with penetrating oil a day or so in advance of the job. I did one side with no advance treatment, and sprayed the other side at that time. The next day I did the other side and the nuts came off quite easily compared to side one.
Oh, another thing. There were cautions about not letting the old bolts spin and ream out the holes in the hangers. Well, if they want to spin, it is awful hard to stop them. It's almost impossible to balance the force on two wrenches so that the one does not move at all. What I'm saying is, mine spun. But, there were no ill effects. The give seemed to occur on the old serrations, not the holes. The new bolts still needed full force to press into place. So I'd say as a practical matter, don't worry too much about the bolts spinning.
Overall I think the job was easier than I expected. I did buy the ball joint tool and it helped. This thread was the biggest help, though! :C
