On the passenger side of the transmission, there should be a tag riveted to the case. It will have a 2 letter code.
Sometime in the last 56 years, someone converted it back to fixed pitch. Not unusual. https://www.v8buick.com/index.php?threads/vp-converter-trans-visual-id-guide.143723/
If you still have the switch that connects to the carburetor, then it would have controlled the switch pitch and kick down. You'll need to find which contact on the switch goes 12 volts at wide open throttle. https://www.v8buick.com/index.php?threads/65-cat-kickdown-switch-pitch-etc.358669/
I get it now just got the car a couple of months ago so still learning thanks for the info I go to Belmont race track a lot for work