Rebuild or replace with a new or rebuilt short block? Who has the best deal?

This is one of those "DUH" things. I overfilled my 6 year old 21hp Intek engine during my last oil change. Got distracted, didn't really realize it at the moment. Thought the engine would just burn any excess oil out of the engine and that would be the end of it. Well apparently not.

Now it's burning oil all the time. Fresh oil immediately turns black as coal. Yesterday I was mulching leaves and the engine started to sputter. I pulled the spark plug and it was coked up with ash deposits from where it's burning so much oil. Gave it a good bead blasting in my cabinet and mulched some more.

Apparently overfilling the engine with oil will damage the rings. According to a guy I work with who works on lawnmowers.

I'm hoping I can keep enough "used" oil in this engine to prevent it from seizing up until I can finish mulching up these leaves. Then repair the engine this winter.

Question:

I have not talked to my co-worker to see how much it would cost to fix this engine.

I am mechanically inclined but out of all the things I've done with cars and mowers, I have never actually installed new rings in an engine. Other than putting together rebuilt short blocks and cylinder heads in cars and dropping them in.

I'm not sure if that's all it would take to control the oil burning. Did I screw up the valve seals along with it?

Any chance I just messed up the PVC system and that might be why it's burning oil? I know that there is a diaphragm inside the PVC box on the side of the engine and if it goes bad, it will such oil into the breather and blow oil all over the engine (seen it happen on a Tecumseh) but not sure if that would cause the engine to burn oil. I suppose I could look in the breather and see if I see any excess oil.

Or is that wishful thinking?

Now might be a good opportunity to learn how to install new rings in an engine! But my time is limited.

My idea would be to buy a new short block and transfer all the bits from my old engine over to it myself. Or tear the engine down to the short block and take it to him and have him install new rings or whatever else it needs. To save some money.

Can I even buy a remanufactured short block with or without a core charge?

I'm trying to weigh the cost of someone else's labor versus new parts.

What's my best option?

I don't have the model number handy but it's a 21hp Intek vertical shaft engine. Who has the best deals on shortblocks?

What are some of my other options? Or than buying a used engine?

I actually have a good 15 HP Kolher engine that is on an old Snapper with a seized transmission but don't think it would have the balls to turn the blades on a mower with a 48" dual blade deck.

I tried replacing a seized Briggs 11, 12 or 13 HP (can't remember) engine on an old 1979 Snapper with an 8HP Tecumseh engine and if the grass was more than 6" high, it would stall the engine. So I think the same thing would happen with this Craftsman mower if I drooped down from a 21 to a 15 HP engine. I'm not sure if I want to go that route.

Rebuild or replace with a new or rebuilt short block? Who has the best deal?