there are about 20 variations of the 4.3 since 1985
however assuming you have a raw water cooled 4.3, take the inlet hose from the power steering cooler to the thermostat housing and block off that port. take the 2 or 4 lines going to the exhaust manifolds and elbows and block tee them...
lots of oil on the plugs - that indicates blowby
the one plug is missing its electrode indicting
there are bits of aluminum on the electrodes indicating the timing is off
being points, you have to set dwell before you set timing. so file the points, set dwell to about 30 degrees, then set timing.
First, welcome aboard
Contact your local registration authority. They will advise on steps needed to become a legal owner
Additionally, good boats are not abandoned. Before spending money, check the transom and stringers for rot
