small ball joint or big?

Just remember the joint is about $20 cheaper but you will also need a new upper control arm and spindle to use it which if you are just replacing a worn ball joint makes it quite a bit more expensive.

FWIW, I swapped in 73+ disk brakes into my 68 Barracuda that had 9" drums. I have the big ball joint now along with the 73+ spool k-member and 73+ sway bar that mounts inboard of the strut rod. A dramatic overall up grade in the braking of the car.