So, what is a "custom" car, then? One that is hand welded with driver's position adjusted for one specific individual? Or just a stock car chassis with all or a majority of all other parts picked and chosen at the whim of the builder?
Again, to me, anything that isn't stock is custom.
Main entry: 2custom
Function: adjective
Date: 1830
1 : made or performed according to personal order
says Merriam-Webster.com...