This site is useful, and has some details on the OTR 80. They were a (very) slight development of the 1990s reissues of the 1970s Overdrive model.
Good amps. Combos and heads would be electrically the same.
Do search here for OR 80s also, which were virtually the same, but more often discussed.
Only dimly aware of existence, a dimly existing awareness...
You get a wonderful view from the point of no return.