I've been reluctant to respond to this post because although I have completed this swap I am no expert and had to piece a bunch of sketchy info from all corneres of the interweb to do the pump upgrade.
My 43f came with the original 5Y1 (early) pump.
The body on the 3AJ (high volume) pump is deeper. As a result of this, the new pump gear wheel will require a thinner dish to it. The thinner dish, allows the new pump assembly to align correctly with the other gear on the back of the primary that drives the pump.
The new pump will not work with the original 5Y1 wheel !
I randomly ordered a wheel from a 1991 XTE put it on the new pump shaft and called it good. It works and lines up correctly. Is it exactly the right wheel, can't say.
It would be super if someone with greater knowledge of this upgrade could post up exactly the correct parts and proceedures required to complete this job.
I have also heard people speak of a required gasket???? to complete this job but never heard solid info on that requirement. Modified driveshaft.......never heard of that.
Mine seems to work good but no guarantee that it is correct. A more experienced voice is required to be entirely sure.
I hope you hear from others.