BobzHog,
Hope your post settles the matter of the existence of Chevrolet 4-speed Hydra-Matic transmissions.
If there is still doubt, I would be pleased to post photos of a 1954 Chevrolet 235 truck engine that was machined at the factory to match a 1954 truck Hydra-Matic transmission (photo available) and an enclosed driveshaft, with shorter shaft because the Hydra-matic is longer the 3-speed/4-speed (photo available).
In 1955, the truck Hydra-matic was made for an open drive shaft.
There are other subtle and not-so-subtle differences (as staterd by BobzHog) in the 1/2 ton Hydra-matic equipped trucks: frame cross-bar for rear mount on the transmission (it is a big and heavy brute), solenoid starter, automatic choke, different brake master cylinder and brake line routing, and push-button start on the dash (check for a hole to the left of the guages).
We still do not know how many might have been made. However, if anyone wants posted sales/technical/shop-manual documents describing the Hydra-matic transmission "new in '54" (for Chevrolet trucks), I would be pleased to post a few items.
Tim
