Snag that Cruiser now if you feel like you know what's wrong. Also, join the 3FE email list if you have questions (3FE is the motor in the '89):
http://autos.groups.yahoo.com/group/3FE/
You'll get about the same mileage as your 60, maybe a little better. It'll pull your boat just fine. That tranny was designed for a bus and is way overbuilt.
Also, visit the 60-series tech section here on MUD. LOTs of good info there....