That conversion chart is slick! Should cover your original toilet.
Thetford is still making the Aqua Magic V in both high and low profiles and they are inexpensive and readily available, for example below.
Aqua-Magic V Toilets - Product - Camping World
One thing you may need to be aware of is that the old Aqua Magics had the two mounting bolts at a 45 degree angle whereas the newer ones are on a line parallel to the front of the toilet. So you may have to rotate the mounting flange 45 degrees to install the new one.
Or for a little more money you can install a porcelain SeaLand, which I believe is what the Airstream factory is using now.