The infamous Merc Marine 300 427s. These types of motors seem to pop up at least once a month on e-bay. Some know-it-all car guy has usually told these unknowing boat owners that they have a gold mine sitting in the back of their boats. So, with visions of dollar signs dancing in their heads, they place these "Shelby Cobra Engines" on e-bay. Here is the reality:
The only really useful part of the entire engine is the block, and even that is hamstrung.
It is a side oiler casting, but was never drilled for the side oiler
oil passages. They are center oilers like the 390/428.
The rest of the internal components are basically 390; cast iron crank, small rods, cast pistons, early 390 heads, etc.
One good thing is they do have heat exchangers so the cooling system is not damaged by salt water.
They are worth whatever someone is willing to pay. Real world value is about $3000 to $3500 for the pair, if they are standard bore. If they have been over bored, their value drops dramatically.
HTH,
--Mike