Pre 1945 Block Cams

[rotorwrench]

The early 99 series till 1941 have the core sand removal ports and associated bulges on the pan rails. The 19A block for 41 was changed some with the abbreviated intake deck area and the lack of core sand clean out ports. The 29A engine of 1942 was continued to some degree during the war for some trucks and the T16 Universal carriers so there were surplus engines at one time. Most of that stuff has dried up in this day and age but they still show up now and then.
http://www.robertsarmory.com/T16.htm

There were some 59 series blocks made with no "59" on the half bell but they are not common. They have all the 239 CID 59 series characteristics. The 41A blocks that were made as replacements for the 221 CID blocks during the war, were continued after the war for a time with the 59 marking on many but they have all the 221 characteristics for the smaller pistons.

It has been said that the 99A blocks have the thickest cylinders of all but some folks mention that that changed in either 1941 or 1942. I've not heard of anyone doing a comparison of thickness using ultrasonic devices but it would answer the old question about this. They are still descent blocks but the 59 series with the new valve spacing was also a definite improvement.