It is indeed likely a 427, note the lack of external harmonic balancer, which the 428 would have for sure! Some have taken the Marine block and drilled out the 'side oiler' passage to make a 'side oiler' out of it. Strange it doesn't appear to have the cross bolts on the mains... Yeah, '68 would be drilled for hydraulic lifters, normally, but it could easily have come with a solid lifter cam. Either will work, just use restrictors in the hydraulic lifter
oil passage. These Marine engines can sure be a head scratcher. Interesting motor, nothing wrong with a Marine engine that can't be addressed during a rebuild.
As to the internals, I would guess someone has pulled the pan to verify the 'innards'? Wouldn't surprise me to find a steel crank in it.