Chocolate Frosty Came Out of the Oil Pan!!!

About 6 years ago I decided to try to get my dad's old TO-20 running again. It was sitting out in his field with no hood on it and to my dismay, the oil filler cap was missing an he had stuck a rag in it. So, the rag became a wick and filled the oil pan with water. It froze and the sump cover and bolt was laying on the ground because the water had frozen and split the bolt that holds the sump cover on (it is hollow). I found parts to put it back together and got it running again and used it that summer to cut and bail some square bales of hay.

I parked it about 3 years ago in the barn and it has been sitting there since. This week I decided to get her back out and get her back in running condition so that I could do some bush hogging. An new battery made her fire right up so I drove it down to my work shop. I refilled the radiator and found a few external leaks that I can fix. I pulled the oil dipstick and it was brown. I tossed a catch pan under and opened the oil drain plug and it looked like a super thick milk shake came out. It was so thick that it would barely filter down into the oil pan. I know this means coolant in the pan.
I also know that my dad did a lot of things to this old tractor a long time ago. If I'm not mistaken, he put liners in the cylinders and ran bolts through the block to pull the block together because it had a crack in it. He used it a long time after that.

I have no idea how to check that repair being that it is in the block somewhere. Is there anything else I can check on this motor, before I consider stripping it to the block, that might have been damaged at the same time the oil pan froze? Could a blown head gasket fill the pan with coolant? Any other suggestions?

If nothing else checks out, and it is the block, is it worth messing with? Anyone know the process to fix a cracked block or do you just have to find another one? Is that so difficult that I might as well turn it into a yard decoration and buy another tractor?

Any suggestions or advice would be greatly appreciated.

Something you might try, before dismantling the cooling system, try to put a little pressure on the radiator.

Pull the plugs and spin the engine through, see if coolant is in any of the cylinders.

If not, drop the oil pan, look up from underneath.

Could be a cylinder sleeve oring leaking or the block.

It takes very little coolant to make the oil brown and you let the tractor set for 3 years to get that much. I'd suggest you change the oil, run the tractor for a few days, then change the oil again. If you plan to leave the tractor set for a long period, drain the radiator and block.