farmall 450 water in oil

I have a farmall 450, I just rebuilt the motor with a block that had been checked for cracks and had none. The cylinder was resurfaced and had no cracks.After putting it back together I ran the tractor for about 4 hours checked the oil everything was fine. Ran it yesterday for about an half hour checked the oil and it had antifreeze in it. Any ideas on what is causing this would be greatly appreciated.

Coolant can get into the pan in three places:
The head gasket, the cylinder head, and the block.
The cylinder head is a first and cheapest hope.
The coolant passages in the gasket interface with the the oil return openings in the block. If the gasket leaks, it will be pretty easy to find.
The second place is a crack in the head through the coolant passages into the valve area, or the oil return openings where the pushrods go down.
The block can be cracked behind the sleeves.
(I assume you did not remove the sleeves, because you indicated resurfacing the cylinders.
This engine has dry sleeves which are a very light interference fit into the cylinder bore casting. If the engine was rusted stuck, or had water freeze in a cylinder, it could be cracked behind a sleeve. Water can get from the crack past the sleeve into the crank case.

Analysis;
Remove the oil pan.
Use a radiator test air pump to apply pressure to the coolant.
Use a good flashlight to carefully look for coolant coming from the bottom of each cylinder sleeve. Look carefully to be sure it is coming from the thin margin of the sleeve and not past a piston.

If none, look for coolant coming down from the cam side area. If yes, Take off the valve cover and use good light to check for visible leaks in the valve chamber and down the pushrod holes.

If none is visible from the top point of view, it is probably the head gasket.

A treatment with Bars Leak or Subaru water treatment leak preventer. might stop the flow.

I would give that a try, as it is least expensive.

It also might get it through the winter, allowing a more temperate repair. Jim

Thank you for the information, Millard

Bar's worked for me twice this past year. it's the easiest "fix" for that "what's wrong with my new engine" worry. Mixed mine with hot water, then added to radiator. Don't forget new filter and oil of course. Now I wonder how to reclaim
this water/oil mix....

Thank you for the Bars Leak idea. I"m going to give that a try.

Jim, Is it possible that the head needs to be re-torqued ? The oiled was checked after being ran for 4 hours it was ok. 2 days later the oil was checked after being ran for 1 hour and water was in the oil.