Anyone know the "critical distance" for a Porsche 911?

I am converting an '86 Porsche 911. I got it without engine or transmission, so I was not able to measure the "critical distance" between the engine face and the rear of the flywheel. I've since purchased a 915 transmission, and have a flywheel with the 9-hole mounting pattern.

So, does anyone know the correct critical distance, before I try to find it by trial-and-error? Thanks in advance for any help.