58 Merc big block

Hope you can help !
I have a 58 Merc, with a big block. Engine cast # 4-7BR1. The guy I got it from swears it's a 430 intercepter , it's in a Monteray 4 door. It will smoke the tires, and has either a limited slip or posi ( Two dark black tracks behind car ! Any info would be appreciated .
Bill

If memeory serves me, the 430 LEM motor was exclusive to the 1958 Mercury Parklane. You could get the 383 as either an option or standard equipment in the other models.. The engines are externally identical.

John