If its on its original chassis id put the farm on it still being on the original fuel line!

that will be the problem as unleaded made it go like glass so itll be split.
A meter of SAEJ30 multi fuel line off Ebay 5.6mmID (which is some random 94/67th in old money...or something like that) can be had for a £10er and will do the whole car. 5.6 doesnt need clips, 6mm which is actually the larger 1/4" is too big and falls off, "Silicone hose world!" is the search word

you need to drop the tank see other threads for that
Sean

A quick check to see if there is a split in the tank top pipe is to separate the rubber pipe from the plastic pipe at the front where it goes up to the fuel pump .. the petrol should syphon out of the tank but no petrol = air leak simple If it runs slowly blow up the plastic pipe to check for a blockage