It really depends on how much horsepower your big block has, along with how high the crankshaft centerline is located, along with ride height of the car to where the starting point is. As with my car (a tube chassis Monte with 108" wheelbase and crankshaft centerline at 12" with about 800-850hp), a rough rule of thumb is to start with the bottom bar almost level but down a little in the front and then have the intersect point at about 45-50" out.
I take all of the measurements and plot it on the floor to calculate which hole in the top front will give me this IC. I make sure that the rear end is square in the car and then the top left bar is then adjusted to give the correct pinion angle (about 1-2 degrees) and then the top right bar is adjusted to give your preload. It is best to start at 0 preload and then if the car goes to the left you will need to lengthen the top right bar and if it moves to the right then that bar will need to be shortened just a few flats at a time.
JMHO
Bill