With buying the engine ? Or after ? 12k is going to be cutting it close if that’s excluding the engine purchase .
Still need transmission to support the power - manual or auto ?
Fuel system , pump lines fittings injectors etc
Build a rear to support the power
Brake upgrade if it isn’t already done
Then you need a power adder . 427 isn’t a small motor so you’re stuck with - Vortech ysi , procharger f1a or something like a b>urbo kit . All in the 5-6k range for a kit .
Then you still need a efi system capable of running what you’re looking to do .