Since you are in the UK I assume it would be quite expensive to get a new or even a used tank. If it were me I would remove the tank and clean it out. Lacquer thinner works real well on the gum and phosphoric acid will dissolve most of the rust if there is any in it. You can inspect the pickup tube with an inspection mirror thru the hole where the sender goes. If you find it has a hole in it you might be able to seal it with some sort of fuel proof sealer. There is a sealer we use on aircraft tanks called Pro Seal, it's expensive and has a shelf life but no fuel I know of will get past the stuff.

 

Just a quick update.

Still haven't solved this, but I have just ordered some copper fuel pipe, and a back-to-back brass bulkhead threaded connector.

I'm hoping to fit it onto the plate of the sending unit, and then attach a run of the copper fuel pipe to the bottom of the tank. (I don't want to go drilling into the tank itself, so this way I can remove the sender and do it elsewhere - so hopefully it will fit on there - I can't remember how much space I will have to play with!)


I plan on putting an inline filter straight after this, before connecting up to the existing hard-line, and blanking over the old pickup tube.


Hopefully this will be enough to stop it blocking, I can't really find anything suitable to use as an in-tank filter on the end of the new pipe.




I'll let you know how it goes!

 

Still plodding along with this one.

I thought I had got somewhere, now I'm not so sure.

My bulkhead connector didn't fit on the sender plate, the hole into the tank is surprisingly small!

So in the end I have made a new copper pickup tube, and soldered it directly to the sender plate. And with a little bit of bending and filing of the cage around the float arm it all goes through the hole and bolts in!






Rubber fuel hose then directly clamped to the end of this, with an inline plastic filter inside the cab.

For now, while I am testing, I strapped a fuel pump to the seat mount, and ran a short section of copper pipe through one of the bung holes in the floor pan, with rubber hose both sides. From outside it ran straight to the carb (with another filter).

I ran this idling on the driveway for a few hours, until it was below the point I think it would have cutout with the old tube, and all was good.

I then drove 12.5 miles each way to an exhaust shop, no issues there.

Then a little 2 mile trip from home, the truck stops on me and won't start. Under the bonnet (hood) there is no fuel in the filter, but there looks to be plenty siphoning into the filter in the cab. But no leaks anywhere, and the pump is going.


Swapped back to the old fuel line and pump and got it home ok (even with the fuel level below where I thought it used to cut out..?).


Took the hose off from the output of the new pump, and a tiny dribble was coming out, so I assumed the pump gave out.

Swapped all the new pipe run onto the old pump, and drove to the garage to fill up, ran fine there and back. Went to reverse onto the driveway and it cuts out and the filters under the hood are dry again.

Left it a couple of minutes, and flicked the ignition back on and it starts pumping through again....

I wondered if it was flakes of rubbish blocking the end of my new tube in the tank while being sucked, then floating off once everything has stopped to let it run fine again, but there is normally fuel in the filter in the cab when it cuts out.

Now I'm at a loss...! Help?

 

My '64 was doing exactly what your truck is doing. It turns out it was flakes of rust blocking the inlet inside the tank. I've chosen to adapt the '67-70 Mustang tank to the frame behind the rear axle and run new fuel lines. I'm custom fabricating a filler neck to come out behind the license plate like a classic '70s GM car.

Your best solution is to replace the tank in whatever way will work best for you.