i have a 75 c10 an it has a 350 and i looked up the vin and it said it had a 454 originally and than i looked at my rear end and its a 12 bolt?... soo did they originally have a 12 bolt because a lot of people i talk to have the 10 bolt and its makeing me wonder.. is it orginal and if so what gears were in them all i know is i need to pull them out and redo them but wondering everything i can about my baby!