In 1934 the 8 cylinder engine was introduced with a water side plate cover. This plate and the core plugs to follow were used to extract the sand from the casting. The side plate style of block ran to sometime early to mid 1935, when at which time the factory introduced a 3 large core plug block in what must have been a fairly short run. Next a 5 core plug block was introduced; with 3 large and 2 small plugs. It also had additional bosses and casting that facilitated moving the supercharger to the right side of the engine, with the intent of a conversion from left to right in the future. [Changes to this paragraph 5/16/18]
All engine block assemblies carry part # A90458. No other part number has been found for designation of the various types of block.
Five freeze plug engines were superseded by a 3 freeze plug variety which ran until the end of production in 1936, making these rare.
6 cylinder engine A90425 started with a water side plate in 1934 and changed in mid 1935 to a 5 core plug version.
There are no known 6 cylinder 3 core plug engines.