Well phooey! The kit(s) will not fit our older mowers, specific fitment to the new 'Select Cut' mowers. Stay safe...we're shelter-in-place in Marin, but we can do yardwork, so far at least.
Youtube has videos of folks that were able to make the new dual-blade system from Ego fit on the older models....So I gave it a try.
1) I got it to work and it made a huge difference in the cut quality.
2) The You Tube Videos were not complete descriptions of how to do it.
On the dual blade system there are two holes on each blade that need bolts through them to make it work. I ended up using 1/4" machine head screws.... but I had to modify the heads with a grinder to make it fit.
This kept the screw head from interfering with the bottom of the motor assembly. At first I was thinking the result was kinda sketchy, but then I realized the machine head screws did not need to hold the blades together.... they only act like pins to keep the blades from spinning relative to each other. The big bolt on the main shaft holds the blades on and together.
The original set-up had a washer with a notched center hole to help keep the blade from spinning on the shaft.
With the dual blades, the washer can not catch the shaft. This worried me a bit but I replaced the notched washer with a couple of thick fender washers and it seems to work well.
(Without more pictures/drawings, the above probably does not make a lot of sense, but once you take the old blade off and try to install the dual blade it will make perfect sense)
The resulting blade system sticks down farther so you must raise the deck to get the same height cut.
The end result was not what I would design and if I had a machine shop I would do it differently. However, it works very well so I am happy with it.