Cheers Nigel, I've got a NOS fuel sender that's identical to the one I just destroyed today, it wasn't giving a reading on a gauge and was gummed up, the filter was in the bottom of the tank too but easily retrieved. I'd tried a bike handbrake cable through the various pipes on the tank but struggled to get it through these 2 pipes inside the tank - until I found a piece of copper brake pipe I could pass it through and then bend to get at the ends of the pipes through the sender hole. I suspect they're just full of crud at the moment and that the tank cleaner will dissolve all that.
The idea of an old speedo cable is an excellent one - I was thinking of using a dremel cable, it's the same thing but an old speedo cable is a much better idea plus it's disposable! I think I might even have a bit of old fire extinguisher pipe to use as a guide for it. I feel a plan coming together!
I was struggling with getting a bung to seal the filler pipe too, I thought about a cork from a home-brew place or a rubber one but couldn't find one nearby. Then I realised I had a spare filler neck with the rubber connector pipe still attached. And a top from an old caustic soda bottle was a great fit, especially when clamped on. I just need one short length of rubber pipe to seal a pipe and the work can start!
Guy