I was at an auction last night and they had a lot of automotive parts & tools for sale aswell as a lot of other things of course . I seen these and no way to look them up . 2 brand new gas tanks still in the box ;
That is an M body tank. Also fits April 79 to 80 f body. Don't know the J \, but it too would probably fit.
Some of them had some weird coating that was not too good for snow or salt / rust.
There are some made now that have electro static / powder coat- ya never know.
would also fit the late 77 and 78's just would have to bump the trunk floor just a little for the rollover valve and extend the vent hose to the rollover valve.