the short answer is yes, most parts are interchangeable. where you have to watch out is things like changes to hinge pin sizes...So you have a cal2 but you want to run the 3.1 rear a-arms. the 3.1's use a larger diameter inner hinge pin (and outer IIRC) so you have to update the rear suspension inserts as well.

I would suggest downloading the manuals for the cars you are looking at and start cross referencing part numbers and info. I did this when starting with my Cal2 and it gradually morphed into a 3.1 and now a WS based SO1.0. If I had to do it all over again and buy once cry once, I should have just bought whatever the latest released car is (SO2.0 currently)