Oil Filter Boss

I have an 88' Caprice carburated engine I purchased. When trying to install an oil filter on it, there is an o-ring in a groove in the filter location. When I put a filter on it, it blows the rubber out and promptly pumps all the oil out onto the shop floor.
I have NEVER seen a SBC with this "o-ring" thing where a flat machined boss should be for a standard oil filter to seat against.

Any ideas? Does this mean this had an adapter for a remote filter or cooler?

I just installed this engine in my 89' Shortbox S-10 inplace of the 305 I put in earlier. It replaced the all but dead 4 banger/5 speed.

Sounds like the last time someone took the oil filter off the filter gasket got stuff on there.

Do I feel like "stupid". I went back out to the shop and armed with a hooked scribe, picked the "0-ring" out. Hmmm, no groove. Stock boss for a filter.

Put on a new two quart filter, refilled the crankcase with 5w-30w and refired the engine. No leaks, runs fair. Now to tune it up and then go see how fast it will go. Then I'll face cleaning up the oil and grease sweep mess in that bay of the shop.

I sure love power in a small package. Next items will be picking the right camshaft and high rise.

One thing about having this Caprice 350 engine in my S10 is I don't have to pull it to change the cam. Lots of room up front after I take the radiator and grille out.