Hi all....I have a 70 with a 12 bolt, 2:73 rear. Can I upgrade to 3:73's without having to change the carrier? What carrier do we have in our cars? Im looking in my Summit Catalog and they list 2 3:73's for a GM 12 bolt. One of those says "fits 4 series carrier" next to it, and the other says nothing. These are Richmond ring and pinions. Also, whats the general opinion on 3:73's? Too much? I do plan on swapping in a 200-4r also. I know with 3:73's and the th-350, highway driving and gas mileage will take a big hit. Thanks for the input.