Can you upload a pic of what you have now? I know the CB750L seat is pretty decently sized for 2 up riding. Here's what was on mine:
The big difference is the attachment for this seat: there's a single bolt near the end of the tank, and 2 bolts on the sides near the tops of the shock absorbers. If your bike has a swing-up attachment, it'll need a bit of fabrication to get it to work. I've got a couple more pics: if you would like them, send me a PM.
I'm sure you can find something on the net somewhere. Hope this helps.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.