Hi, Gauntjoh.
And just about exactly equal to TWO D9Ts.

Thanks for the updates.

Just my 0.02.

Last night I finally finished scanning one of my highly prized Caterpillar indices "Caterpillar Serial/Product Identification Number Index". It took me some time to figure out how to use it and its limitations. 
The main part of the indices is where the engine and chassis serial numbers were the same. Then by the time this booklet had been published, in 5 of 1990, chassis, transmissions and engines had become personalized to different models and applications with different prefixes and suffix markings. I found this booklet covered all the beginning of Caterpillar, Best, Holt. A special section helping convert WWII Military Serial/Product ID Number Index to non-military equivalent indexes.
The last chapter I found very helpful when looking for comparable and compatible engines. Post 1960-1964
I found it my go-to manual when questioning any Cat, Best, Holt S/Ns.
Should be in the library soon. Thanks