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Went to NAPA to try to buy a water pump for the 1956 235" in my 49 half ton. This pump has an external impeller which goes into a large hole in the block.
NAPA has photos on their web site of the pumps which helps greatly.
The pump which fits later model 235" with the external impeller (like mine) has a 5.25 inch shaft, measured from the mounting surface to the hub.
The other pumps which have the impeller intenal and covered with a flat plate measure 4.125".
I ordered the former but when I measured my shaft length it was much less than 5.25". Therefore there must be another pump available like mine but with a shorter shaft. I do not think mine was modified because it was done more than 12 years ago and I wonder if they even modified them back then.

I used napas #58-126 (1953-1955 235 chevy car 3/8" pulley) water pump coupled to predaves adapter plate in my 1951 suburban.I have a 1956 235 engine in it.I think there is about 3/8" to 1/2" clearance between the fan blade and the radiator.I can check if you need to know the exact measurement.

Can you post some pictures of your water pump ?

Thanks,Tim

Tim the pump is still in the truck but if you go to the NAPA web site and look for 1956 water pump for Chevrolet you will see it. Its the one with the 5.25" shaft listing and has an exposed impeller.
I understand that Patrick's makes the pump the way mine is.

I have the stock water pump that came off of the 1956 235 car engine that is in my suburban.I understand what you are describing.I purchased the adapter plate and the short shaft water pump to properly place it with the radiator.I'm not familiar with Patrick's water pump.

The way I understand the adapter plate is that it blocks the big hole in the 235 block and the pump with the internal impellers can be used.
I understand that Patrick's pump is the same as mine but with a shorter shaft.

"They" have been modifying the later pumps ever since the first "they" installed a later engine in an older truck. We used to have to do it ourselves. Now you can buy them already done. If you can find a 292 Ford pulley and have access to a press you can do it yourself and save a bundle.

Just an aside, Napa part number WP-5815 shows that it is COUNTER CLOCKWISE rotation I hope this is a type-o

Cletis can you explain the process a bit more please. I assume (bad word I know) that once you have pressed the pulley farther down the shaft tou would cut the remainder off.
Why a Ford 292 pulley?

The Ford pulley is close to the diameter you need. The pulley on the 216 is too small which will cause the pump to run too fast. There are other pulleys with the same bolt holes and larger diameter but I don't know specifically what vehicle they came on. You need one with a diameter close to the pulley originally on your engine.

After pushing the hub closer to the pump the excess shaft can be cut off with a cutting disk.