[SFfiredog]

Looks like you have a '66 marine 427. These were common in Chris-Crafts and the likes. The block is cast with side oiler cores but as you already know, it is only machined as a center oiler. The heads are 390, as well as the cast iron crank and small rods. The only good thing about a marine 427 is the bare block.
Even if you wanted to go through the time and expense to drill it for side oiling, all of these blocks I have seen have had a big machining groove cut into the side oiler rib on the LS of the block.
It looks like they did it when they (Ford) machined the motor mount pads. Unless you are running Le Mans or Talladega, the side oiler block is only really useful for bragging rights.
HTH,
Mike