I am in contact with Dennis and just sent him some information (in German :-))
Have you checked this web site:
http://www.wilcap.com/flathead.html#FHID They provide a lot of helpful information about all the options he has with different gear boxes and/or bell housing adapters. The three speed gear box adapter to the 59A can be found here
https://macsspeed.com/index.php/prod...d-49-64-detail Please note that the clutch finger sits on a cross shaft and he probably has to modify his clutch release arm. Good luck.