will a gas tank from a 1984 xj6 fit a 1977 xj6?

quite a bit of difference in year modle and body changes i doubt it will .i would try calling a dealer or a shop that works only on forighn cars.

Call your local junkyard or auto parts store that has a Hollander Interchange Manual. The Hollander manual will tell them if these parts are interchangeable. Or, you can check www.car-part.com and see what years and models come up on a search there, this will do basically the same thing.

i have a 1975 jag series 2 i replaced my tank with one off a series 1, you have to make sure the sender unit and the petrol feed pipe are in the same place take heed that is the most important part other than the mounting bolt holes, some tanks have the sender unit holes at the back and front so they are usually easy to get round mine had a breather coming out of top rear of the tank but the replacement one didn't so i had no where to connect the breather up to so i left it off but it hasn't seem to give me any trouble the first thing to look out for is weather you have su pumps in your boot or the pump is fitted in the tank with the with the sender units. so dont get mixed up thinking the drain plug hole is the feed pipe at the bottom of the tank the new tank i fitted was slightly bigger than the old one but as long as the mounting holes are in the same place didnt seem to matter with an extra little push with a jack

Both fuel tanks on these are very similar except the intakes and fuel measure systems are located slightly different, I think your asking can you use them on both sides in a word NO

No different sizes