chevy 37,
It really depends on how many MILLs ( thickness) of paint is on it now.
10 Mills is really the limit for a paint job lasting for any length of time, after that it will chip easy, start cracking, top layer will soak up & loose its shine, ect.
You can drive your car to the local PPG Jobber & they can check the Millage for you( with a MILL Gauge) to give you an idea how thick the paint is.

If the body is in decent shape ( meaning not alot of dents) you could block sand dry with 220 grit sand paper to cut alot of that old paint off & in the process making your panels straight !
Then reprime with 4-5 coats of PPG's K-36 let set a couple of days & sand with a wet block with 400-600 grit paper.
then seal & shoot your prefered flavor of KOLOR.( This is what I would reccomend)

Or you can just DA sand the whole thing down & wipe & shoot
just like Earl Schibe or Macco

Getting a quality paint job is not an easy task , it requires alot of work, and elbo grease.
Spray