Question about engine models

I am interested in buying an rv 6 kit that is almost ready for a powerplant. I am looking at both 320s and 360s. I am finding some reasonable deals, but I get confused with the sub-models (io360 a1a, a4a, c1e6 and io320 e2d, a3b) I just want to make sure I don't buy an engine that wont fit, or buy something that will take a lot of modifications to work.

Thanks in advance fellas.

Wikipedia

Wikipedia has a comprehensive list and what they mean.

Engines

What prop do you want to use. Some 0 320's and a few 0 360's will not accept a constant speed prop.