What size battery ?

Any decent "parts guy" can look this up. These were originally "group 24" not to be confused with Ford group "24F" which has a different lower clamp flange, and the posts reversed.

It "used to be" that you needed about as many CCA amps as CID, IE a 400 cube engine should have 400 minimum or more CCA

Go by WEIGHT. If the pimply faced teenager at the discount store gives you the choice of two warrantee batteries, and they weigh about the same, you are getting screwed.