The A-A Split Shift Spring Kit will get the 1-2 shifts closer to the 2-3 WOT shifts. But if you are very particular in getting both of the WOT shifts exactly the same, then you need to start testing the springs in the valve body.
The 1-2 shift spring and the 2-3 shift spring. They are both different sizes and they can be different sizes from one valve body year to the next (per Rick Allison from A&A). You just need to pull your existing one to see what it is.
When I started messing with mine I just pulled the existing spring out that I wanted to increase the WOT shifts for and I pressed the spring down on a digital scale to see what the max pressure was before coil bind.
(Is this the best way? Probably not but I needed a starting point.)
Then I bought some springs that measured the same outside diameter and referenced a spring catalog like Lee Springs. Then I bought 4-5 springs that were what I thought would be a "little" heavier than the one that was in it. When I got my springs I did the same spring test on the same scale. Then I chose the spring that was 2 lbs more than my existing spring and then test drove the car. What I noticed was that the higher the 1-2 spring rate got, the higher my light throttle and my WOT shift rpms became (keeping the same governor and throttle presures). Then it became testing the springs until my 1-2 WOT shift was the same as the 2-3 WOT shift. I now have both matched at 5800rpms.
I also delayed my 2-3 light throttle shift points the same way. I added a little heavier spring in the 2-3 shift spring bore and this did delay the light throttle shift. But, it also delayed my 2-3 WOT shift a bit. So I then got my 2-3 light throttle shift where I wanted it and then reset my throttle pressure to give me the 2-3 WOT shift point that I was after, then I went back to the 1-2 shift spring to dial it back in again to get me the 5800rpms per shift.
This did take some time to dial in the shifts but I now have even WOT shift points.