If you are going to build your own do it the way Cab Burge says to do it. A cardboard template using some kind of studs in the intake to get the eight holes and then transfer it over to the metal piece to be used. The more holes you use in the intake to attack a plate will divide the weight of the lift or the motor between all eight studs. It is not the carb corner that are different it is the carb spacing between each carb. This should be the intake you have on your motor.

http://www.stagev.com/images/MN2-4BBL-426.JPG