First, I agree with HL's opinions regarding changing this out.
Nonetheless, I think these are answers/clarifications to HL's valid concerns:
1. "The hole in the firewall is considerably larger on the HydraMatic-equipped trucks for extra bell-housing clearance The hole in the firewall is considerably larger on the HydraMatic-equipped trucks for extra bell-housing clearance, . . . "
-- The hole in the floor/toe-board is bigger because the floorboard hole and cover is bigger. The "geometry" of the floor/toe-board is not different. A special floorboard cover (larger) is needed for the Hydra-Matic because the floor-opening is bigger and thus an accelerator pedal is mounted on the cover, not on the floor.
2. "there's a solenoid-type starter instead of the stomper"
-- Not really a problem. As long as you have the the "snout"/cover at the front of the starter, rebuilt starters are available (Chevs of the 40s). Also, the push-button starter-button for the solenoid starter can be placed anywhere on, or under, the dash.
3. "the crankshaft flange bolt pattern on the engine might possibly be different, (not sure about that, though)"
-- I think that there is no difference in this regard between Hydra-Matic and manual-transmission 235s. Nonetheless, the engine and transmission were "mated" at some time during assembly. I assume there might have been some fine-tuning (machining) of the mating-surface on the 235; but, people have successfully put replacement 235s (or non-standard 261s) up against a 1/2 ton Hydra-Matic transmission (engines that were not originally matched to the Hydra-Matic).
4. "it's going to be difficult to adapt a clutch pedal and linkage due to a different-shaped frame around the bellhousing area."
-- The regular post/pivots/pedals-assemblies for manual-transmission trucks bolt right into the same hole in the frame.
Greg_H is better versed in this - maybe he will post his comments/clarifications/corrections?
If you sell your Hydra-Matic parts, you should be sure to include (if possible):
- engine
- Hydra-Matic transmission
- the open drive-shaft will be a different length compared to the drive shaft on a 55-1st 1/2 ton manual-transmission truck
- all the shift linkages and the steering-column shifter mechanisms
- carburetor accelerator linkage and rods from carb to transmission
- a automatic car-carburetor will be needed (it also has an intake-manifold stove-heated automatic-choke)
- frame crossmember at the rear of the engine (it is a bolt-on)
- frame crossmember at the rear of the transmission (it is a bolt-on)
