You're going to remove your 23-year-old tank, sell it to your friend, then install a new tank and sell the boat? WHY???
Sell your boat, have your friend purchase and install his tank. The former makes absolutely no sense.
Typically a new tank is a selling point on older, larger boats. Particularly if they're cast or fiberglass. Aluminum tanks can oxidize and develop pin holes over time. I doubt you will recover any of the cost of parts and labor for the tank replacement.
Not sure why anyone would go through the trouble of INSTALLING a 23-year-old tank.