I don't know how many versions of the 4.3L block are out there so you would have to be sure you find a compatible version and replace the steel freeze plugs with brass blogs. You will also need new marine head gaskets.
Beyond that, a remanufactured short block from a marine remanufacturer would be the best way to go if the cylinder heads from your old motor are still in good shape.
Either way, I would strongly recommend getting a factory service and repair manual for your engine and outdrive. There's a lot more to it than you think.
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