Just for your curiosity, zoomed in and lined up as well as I can,
Cataldo JAEBird - current Embassy Pro - current Tbird VP - J-Bass 60s spacing:
View attachment 3676803
What did I learn? It appears that the location of the Embassy's neck pickup is not a problem. And I learned that a bolt-on with maple fretboard was ok with Entwistle, at least at one point in time.
I like J-type but would like to explore the Thunderbird world without committing too much money. I think one Thunderbucker rounted into the neck pickup position of a J-type would let me try it. Not the first person to think of it.
If routing into the bridge position there's a legit choice of higher, lower, or could split the difference. Since I like the J with 60's spacing better (the one with 70's spacing has the bridge pickup lower), I'm happy to learn that I need not go in that direction.