Cab Fuel Tank

Searching the net for a new one.  How many different types are their.  I have found a site that says theirs a GTI and a Non GTI tank.  Does it matter which one I get?  Ive found a GTI one that is a lot cheaper.  How would I need to change the GTI one to fit a non GTI as im running a carb.  Ive found a GTI one that is a lot cheaper.

Thanks

There's 3 kinds. I've listed them before, a search should reveal.