Ways to have fusion parts
First, acquire some bronze keys in live racing. Second, accumulate the totally free bronze crate Donna gives you every four hours. Next, have a part from acquirening a Daily Battle. Also, race every cup & trial race you may to acquire fusion parts &/or keys. Lastly, buy cars as well as strip them for fusion parts (for example, you may buy more t1 Fiesta STs to strip to have fusion parts for your t3 Mustangs with buy more t2 m235i to strip for your t3 BMW M4s). You will not have Mustang with M4 stage 6 fusion parts this way, but rather common, rare, as well as epic parts which are usable on any Ford with BMW cars in the online game (Ford for Ford as well as BMW for BMW). To have stage 6 parts for the Mustang with M4, you would have to strip Mustangs as well as M4s.
If you truly want gold, use csr 2 hack.