S/O or ?

[FWB]

agreed that you need to check bore size.......the lack of oil galley plugs in the back around the cam tells me its a solid lifter block.
marine and industrial blocks were hydraulic so its not any of those.
basically i can tell you what it's not
not marine
not industrial
not sideoiler,
it may not even be a 427, but it might be if the bore is right.
if the bore is 4.236 or bigger its a 427 if its smaller, its a block made to be a crossbolted block.