Vince -- The pictures are so poor that I cannot make out the date code with any precision, nor the relief and spring passage for the side oiler function. It may be a side-oiler cast block, but not drilled for the functioning of the side oiler passages, etc. Too, while it looks clean, it is the water passages and the backs of the cylinder walls that take the salt water abuse. Since it is a block, and not the crank, you don't have to worry about the crank being reverse rotation, which is common on marine engines. I'd suggest that if you are interested in it further that you talk with the seller and obtain much more detailed information in the form of pictures and mircometer readings on the cylinders, the cam bearing passages and main bearings and caps. With any big block Ford you need to careful about "core shift", which while not easy to explain, in case you don't already know, is the tendency for bore core plugs to shift in the sand casting process; meaning the that all of the bores do not align with one another. To test that it is best to have the block scanned for same.
Couple of things that may have been missed by some....
If that is a Lake Michigan run Chriscraft/boat etc, there will be very little effect of the salt in the water. Lake Michigan is fresh water.
There are RH drive and LH drive 427 engines build for these boats. You had to have one crank go the opposite direction to keep the boat going in a straight line...... SO, you really need to do your homework to make certain that someone isn't selling you a "left over" engine....pun intended! Now, the block doesn't care which direction it goes....but the crank oiling hash marks do....to keep the oil in at the rear seal! This can be redone by a crank shop......if you do end up with the counter rotating engine.....cam will be backwards.......distributor may have a different breaker plate in it for counter rotating shaft. Never seen one up close.
Otherwise, these blocks are cast in many different configs over the years and some detective work on the internet,, which you already found the links, and some good work looking at the blocks with the proper tools, and you could find yourself a potent starting point for a 427!