67 Convertible I6 rear end.

[Howie589]

Hello all. A New guy here and I have searched the forum but have not seen exactly what I am looking for. I am upgrading my drum brakes to disc at the front so they will now become 5 lug. I would like to change the rear to disc also. My question is if I put a v8 rear end aka 9" cause that is plentiful around here in order to get the the disc and 5 lug to match front. Do I need to upgrade my rear leaf springs. They are the standard replacement and are a year old. Wondering if the upgraded rear end would make a big difference in regard to the springs, Thanks.