Why are there different sized radiators in 1995 neon with the same sized engine?

I've worked in the radiator buisness for over 10 years, so I can actually answer this one.

There are two types of radiators for the '95 Neon, one for the auto trans and the other for the manual. You can use the automatic transmission radiator in a manual car. Ignore the transmission line fittings. The only thing that flows through them is automatic Transmission Fluid, which will not be there in a manual. Nothing will leak out, unless the radiator is defective. The automatic trans radiator is also a little bigger, but the mounts will move and it will fit. Obviously, you cannot use the manual rad in an automatic car. You wouldn't want to anyway, because the automatic rad is almost always cheaper than the manual.

In '96-99 the neons did have three different rads. One for the manual & two different auto models, determined by where the car is built. If the first digit of the VIN # is a 1, then it is American made. If it is a 3, then it's Mexican made. You can interchange the American auto trans radiator in place of the manual, but you cannot put the Mexican rad into a manual car. You also cannot interchange the American & Mexican radiators.