Hydraulics went only with Power Glide equipped cars.
This allows for the use of the larger, late model fan, which provides better cooling.
(Note: it is not correct to press the early 216 pulley onto the late water pump, since this spins the impeller approximately 190% of design speed, and may even cavitate the water, causing overheating. Your neighborhood parts house has them available.9. Check for the presence of this vital item if you're putting a "stick" tranny behind the later 235!
One interesting fact about the 235 inline 6 is that it was the engine that was used in the first Corvettes that were produced in 1953 and ran up through 1955.
This same engine was also used in GM trucks from 1954 to 1962.
This provided basic power, great dependability, and better gas mileage.