Thanks much Chris. Do have the hatch cover but was leery about the wiring before your explanation. Shopping for the sender now.Hopefuly your boat has a hatch over the fuel gauge. If so, pop it off, and remove the 5 self taping screws, holding the sender in place.
SeaSwirl boats often had a plastic tank, with screw threads moulded in. Be careful not to strip those. Some of those plastic tanks had galvanized fittings. These can rust out by now.