My understanding is,
The base marine 350 (in this case) is nothing more than a standard (typically) heavy duty or not, Truck block. Higher torque at lower RPM based on cam profile.
Marine goes down one line with specific gasket sets, core plugs, water pumps (marine are bi-directional), cast iron manifolds, flywheels, oil pumps (marine are brazed at the pick up tube) and specific oil pans, wind-age trays at the crank (thus special main cap bolts to support the wind-age trays) and associated gaskets and possible a couple other little things, the other line of engines go into trucks.
So the SHORT BLOCK engines are identical and all parts are interchangeable Marine and non marine. With the exception of gaskets and core plugs.
Typically a short block does not come with Intakes, water pumps, oil pans or oil pumps. Only an assembled block and heads.
So when they come out with a "higher performance model" it would typically have a different cam if higher than say 20 - 30 hp above base and a different fuel curve (re-calibrated carb) and/or timing. For EFI it is strictly fuel curves and timing that are changed with the same base block.
Base being 260 hp in this case
20 - 30 hp only above base, timing and fuel are changed only and maybe the intake but I forget now,
Back in the prior years when they were using the non vortec 350 the difference between the standard (260 hp) and the 350 mag (270-290 hp) was only intake I think, (Slightly higher profile) and carb calibration and timing in some cases,
The timing module (carbed versions) would have a slightly different timing curve and a higher advance ( example: 22* of advance which gave a total of 30* standard and 24-26* of advance, 32 -34* total for higher HP.
I did the research on parts between both and all internal engine block parts were the same.
As far as gaskets sets, Go to a Napa and order a marine engine gasket kit for your Votec block. High quality Fellpro gaskets.......!!
. I'm only planning on keeping her for maybe another year before I upgrade to a newer boat.
