I just checked my buddys stock 1970 Coronet R/T yeterday ,it was .5 degree. I'm mocking up my 64 Belvedere its about 3 degrees down in the rear. We are discussing this in the race forum. I agree that the higher and further back,(as long as headers,suspension,etc fits) will be best for traction. Adjust the pinion angle at the rear axle and you'll be set. I noticed my cross ram manifolds carb pads are tilted forward,but my Indy crossram pads are level. I really don't think it makes any difference as long as the angle is not extreme.
Doug