Hi There,yes 79 80 &81 E & S model tanks should fit.I have a S model tank on my 78EC.Alpha Sports may be able to help if you have a lazy US $500 for a new one.Part NO 44110-49020-YD8 ( EC Tank Assembly )Yes the indented tanks are as rare as Hens Teeth.I´m in Australia,Alpha Sports are in USA.Good Luck. Cheers Mark. PS. A Motorcycle Wrecker should be able to tell you more accurately what will & wont fit.The G model tank is deeper but may fit also.