Guys, my brother has this old 1991 GMC Topkick C7H042 truck, with a 366 gas/propane engine. Not entirely a race-related topic I reckon, but if I can get it running I may buy it to convert it to a car hauler.

It has not been run in many years; perhaps close to a decade. I plan to squirt a few CCs of Marvel's Mystery Oil into each cylinder before trying to start it. My brother said he was able to crank it with the starter a couple years ago.

My brother parked it only because he didn't have an immediate use for it, but he didn't maintain it while parked. You know what happens then......

The inside of the 50-gallon fuel tank is a thick layer of rust. I set that aside in favor of a similar GM fuel tank that came from an older, non-fuel injected truck. I'm confident that I can adapt that replacement fuel tank.

The in-tank fuel pump and fuel level gauge is a pile of rust, and I can't seem to find a replacement for it. The truck salvage yards in my area either only have pickup trucks or parts for semi tractors; nothing in between.

I think we're going to try an external fuel pump; Holley recommended their model 12-927 in-line pump. I'm hoping that the stock fuel pressure regulator is still sound.

The truck has I believe 'throttle-body' injection, and I think it needs 11-14 PSI or so fuel pressure.
I know I'll need to install a pre-filter before the pump, and mount the pump lower than the fuel level in the tank.
That fuel pump is $180 from Holley, but I'm open to cheaper alternatives.

The fuel lines are some type of semi-rigid plastic, and I need to adapt them somehow or replace them with something else. As it is, I wish to try to flush out any old fuel or contaminants in them.

I have not been able to find much for technical data, manuals or diagrams for that fuel system, especially with that propane option. The extra hoses there are a bit of mystery, though we don't wish to run with propane fuel, at least for now.

Anyone have any advice or remarks for me please? Thanks a bunch!

To adapt the hard plastic lines you might be able to use compression fittings. I've used them on my freightliner with success at those pressures. pretty sure I got them from McMaster Carr. The type with the stiffener that goes inside the line.

Go ahead and diassemble the tbi and replace the regulator and injectors . Use push lock hose to replace the factory stuff .

11 to 14 psi is correct, you should be able to use a pump from a 3/4 or 1 ton pickup for an in tank option. I agree with replace the injectors and reg after setting that long. As far as the propane system no idea you might try to get it running on that if the lines and mixer appear sound, far less likely there are rust or contamination in that side as it should be sealed from the atmosphere.