How would I achieve a Attachment System?

So, I am trying to build a game similiar to "My Summer Car" and i would like to know how i would go about making a system that allows the player to put parts together, like pistons in a block, and a head on the engine.
and how to keep track of what parts are attached so i can calculate the performance of the parts and the car altogether based on what parts are on it.

 

I just answered a similar question here.