Hot Rods need a measurement

Getting ready to do some work on the A frame.
On a A v/8 I read that the center hole to center hole distance is 4 7/8 '' between the rad mt hole and the hole for the rubber mt for the flat head. Does any one have the measurement for the rad hole to the mt for a hurst mt and a sbc?
I know the best way is to mock it all up and drop it in and get the measurement that way.