Just don't let the FAA catch wind of your undocumented supply chain...

Most warbirds are not experimental so you can't just build whatever you need and slap it on. Sure you can convert to experimental but you still have the high maintenance costs (FAR 43.1(b)(1)) is the section of law you should google)

Edit: someone looked up the tail number and this one got lucky but don't assume you can just slap your own machined parts on a P51 or something without jumping through hoops.