Here we go with the good old CB750 F seat base, designed for the Super Sport model of the good old S.O.H.C. variety.
I have sold many of these and they are pretty easy to fit too, and I am sure that you will like the look of this seat set up.
This seat base has these dimensions: 25 1/4″ long : 7″ high at hump on the rear : 14″ seat area: hump is 11″ in length. Rear is 9″ wide: The seat base as an birds eye view is: 10 ” wide at the rear of the flat seat pan and is 8 1/8th at the front.
There is also a lip at the front that is the correct shape to fit into your Super Sport gas tank.
It has 2 tabs at the rear so you can use bolts or, mount your turn signals too, thus allowing the seat base to swivel up and down if you so wish.