Join Date: Sep 2010
Location: Rupert's Land
Bikes: 1981 Raleigh GP, 1985 Norco Bush Pilot, . . .
The date the frame was manufactured is in the Kuwahara serial number. The first 2 digits are the year, the next 1 or 2 digits represent the month, the last 5 digits are a sequential number.
The serial number is located on the lower seat tube non-deralleur side or a bottom bracket shell.
Not everyone is looking to buy a tandem, so you may need some patients when trying to sell. My guess for a price is $500 -$800