Craig, To answer your question, yes the tank sizes changed since 1991. We discontinued using the Stainless steel tank because some had minor problems with pin hole leaks in the welds. We changed to two tanks connected together. These tanks were marked as 22 gallons each or 44 gallons. Under the engine a wedge tank was used and, if I remember right it was a 23 + gallon tank. These tanks are marked and available from Ronco Tanks.
Roger