I spoke with a plumber and he can order a replacement Gerber tank from the supply house. There several newer designs that have the bolts 6 and a half inches apart that will fit the toilet.
But, will the new tank be a 1.6 flush? As you mentioned above, your 1986 tank probably uses something like 3.5 gallons per flush. If you go to a 1.6, it probably won't work properly. And no, I don't think most new tanks can be modified to flush 3.5 gallons.
I say replace the entire toilet.
Last edited by stephen9666; 04-07-2013 at 08:17 AM.