1969 valiant with 13 inch wheels

What you have is a 5 bolt 4.0" diameter bolt circle with 7/16" threaded lug studs.

Typically the left hand side (drivers side) of the car had left hand threaded lug nuts (reverse thread) if it still has those and your planning on keeping this (small diameter) bolt pattern, I recommend you replace the LH threaded studs and nuts. These are nothing but trouble.

When you say disc brakes all around, are you talking about 4 wheel discs? If so, why? What are the final intentions for the car? Most times a proper adjusted rear drum setup along with front discs is just fine.

I will let others chime in with the rest.
i may only go with the front disc. the car is original and has all new drums but they stick and squeal no matter how many adjustments i have. and they pull to the right if he presses down too hard. he is a new driver and i just feel that disc are safer but i have been told if i put disc, the 13s won't work so i have to change wheels and rims. if i do that, i have to change the rear wheels too, right? other wise the car will slant down. He wants to keep it as original as possible but knows he needs discs.