I have a '58 235 engine (6 cylinder) in my '49 3100. My '58 Shop Manual shows separate diagrams for a 6-cylinder fuel pump and an 8-cylinder fuel pump. The fuel pump installed on my 6-cylinder engine is clearly the 8-cylinder model.

At the time I purchased the truck, the engine was not running, but the fuel pump was working. I know this because I watched it pump fuel into the glass filter and carburetor. This leaves me with several questions. Is this the original pump for this engine or did somebody replace it? In other words, did Chevrolet start using the 8-cylinder pumps on 6-cylinder engines or did the previous owner install the wrong pump? Are these pumps supposed to be interchangeable? The shop manual says the 8-cylinder pump is a higher capacity pump (which I would expect for a larger engine). Can I use the 8-cylinder pump on my 235, or will it swamp the carburetor and engine with too much fuel? Final question is how do I get this dang pump apart. The shop manual says to compress the main spring slightly and unhook the diaphragm from the rocker shaft. No luck for me.