sorry my friend got a dye rino cover for his tank and it fit. just go on ans and look in the tank covers.
The 68ci Rhino cover will probably fit on a 77SL tank, but not on a traditional 77, because it is longer than a 68. I have a 68ci tank, an original 77ci tank, and the 68ci Rhino cover; and the Rhino cover does not fit on the 77.
slightly off-topic but just to confirm, any 68 ci tank cover should fit the 77 sl tanks (i have old 68, 68 sl and 77 sl).