I got a look at a CJ5 Jeep yesterday and the radiator sold to me as fitting a CJ3A appears to be a drop in fit for the CJ5. I looked at photos of the CJ3B and saw they use the same radiator as the CJ3A.
So, in light of this I can say for sure the side mount radiator that Champion sells for the CJ3A is actually for the CJ5 and newer Jeeps. It will not be a drop in fit in the CJ3B or the CJ3A.