I bet boat engines are rated at 260 HP so I would go with the EFI however the 5.7 will have a little more torque.
The carb may need a rebuild on the 1997.
So things to look at are the overall condition, engine health (compression, oil analysis, rust, ...), outdrrive condition (lube for water and metal fillings), corrosion of the housing and chips/cracks.
1997 2400 SCR
5.7 Vortec / Bravo 2