The curse of the run away 64-65 Lincolns… Its the lower shift column bushing. They get old and fall out then your shifter wont go all the way into park and can slip into reverse on its own. The good news is you can get it from Bakers auto for $35. Bad news is that its a pain to change. There is a lot of info on this at thelincolnforum.net
Yeah I think a lot of the bagged cars are running just the 2 mufflers and removing the resonators. I ve got my 64 that way with flowmaster series 44 mufflers, its quite a bit louder than stock that way though.