I did a leak down test and found that the valves are shot on affected cylinders. I don't know if it is worth fixing it or I should just replace engine. I don't want to spend a lot of money. Would it be an option using a Chevy 4.3 out of an S10 or something.
a 4.3 in a boat and a 4.3 from a truck are the same short block and heads
how the motor is upfit is what makes the difference.
you can pull a 4.3 from an S-10 or silverado, however, you have to pull the motor apart, install marine head gaskets and brass core plugs.
you then need to use a marine water pump and all the accessories, intake, electrics, ignition, etc from the marine motor. buy new exhaust manifolds
keep in mind, your boat being a 1988 may have a 1986-1987 engine in it, or it may have a 1988 engine
if you are just going to change the short block and heads. stick with the exact generation of 4.3. which means you are looking for a good running, low mileage 35 year old 4.3. may be easier to find hens teeth.
I personally would build a motor with a 1993 or later short block (with the mechanical fuel pump and balance shaft) with 1996 and later heads (vortec) and the 153 tooth flywheel to match your coupler. then make up some spacers to get the balance shaft motor damper to play nice with your 1988 or earlier accessories.
some light reading on 4.3's
https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/
