I just tried a 1974 fuel splash plug in a 1964 fuel tank and it won't fit ,it's too large ,also tried the bigger plug in Victa 18 , Rotomo , Villers and Kirby and still won't fit.
The tapered red Silicone or (low density polyethylene) T plugs may be ok ,they are about 16 USA cents each if you buy 500.
Not sure how good they would be for fuel as I've never tried them in fuel ,I have a couple of smaller red plugs here so I could leave one in a jar of fuel for a few weeks and see.
One difference is they are about 20 mm in depth. May not be worth buying from eBay as a lot of the sellers description doesn't match the image ,so you'll end up with the wrong ones.
