I think i have just the solution for you: DataAssets, one of the most underrated features in ue4
you make one of those bad boys for each type of upgrade. Engine, wheels, whatever. Then you can add a ton of variables that the types share IE engine would share max speed or whatever. then instead of switching out actors on the main car BP you can just set the information based on the data asset, and it even works for meshes. I use them all the time its basically like a database (actually if I recall it IS a data table)
https://www.youtube.com/watch?v=hcwo5m8E_1ohope these helped!