I have a 4 bolt crank in a 1940 GMC with a 6 bolt flywheel. 2 holes will line up and had to re-drill and tap the other 4. You will have to find top dead center for your timing mark. This gave me a 12 volt flywheel and starter. Have 4K miles with no problems.
Joe

just retired and finally making headway on my project truck. 1940 GMC AC152.