I would butt the yoke you plan to use all the way into the trans then measure the C to C you have at that point then subtract 3/4 from that dimention & this is with the suspension loaded (axle on stands). give that number to your shop. EDIT I would locate the front/rear axle position first & I like to have the bottom of the rear shackles point slightly rearward so that the springs "work" when they are compressed when you get on it as opposed to raising the car when the springs arc over center which they do if the bottom is pointing forward from "vertical". keep an eye on shock fitment when you change that position.