I'm looking at a 1964 Mercury Montclair Marauder. It has a 427 with 4-speed. I'd like to find out if all this is from the factory. It is a Canadian car with the following numbers: 5BB 345 JB and 163C 64L 072721. I've a feeling it was born with a 390. Also, how can I tell if the 427 in there is the right one?