Special/ Heritage fuel tank dimensions, bolt-on to standard?

[arcticXS]

Hi!
As the modifications to my 1977 standard slowly drift towards the scrambler/tracker end of the spectrum, I am considering a smaller fuel tank. According to the specs I manage to find, the standard is around 4 gallons, Special around 3 gallons.
I understand these are directly interchangeable, is this correct?
If so, what is the width of the Special tank, at widest point and at aft end?

I also plan un using some kind of "Brat Style" or scrambler seat, ideally one that is wide enough to keep the stock hinge arrangement. Any tips on where to look? Will an early seventies Honda XL 350 seat be close?
Most aftermarket seats of this style sit on top of the frame rails, making hinge removal neccessary, and I would like to be able to reverse changes later, if I feel like it.

 

[nj1639]

The tanks are a direct swap. The similarities are the fronts are about the same height and the rears are the same width. The difference is the sides and the drop from front to rear. The Special slopes more from front to rear and the sides are a more direct line from front to rear....less rounded than the Standard. It's not a bad idea to have both on hand to change things up from time to time....the Special for sporting around town and the Standard for long runs.