head

would a warped head on a 1948 cub let oil get in radiator

Only if a head gasket is leaking and the engine pumping oil past the rings. In this case you would see bubbles in the coolant when the engine is running. You would also experience other engine performance conditions/problems.

Since a cub is a flat head, there is no oil in the head or at the head gasket. If you have only recently purchased the cub, a good possibly is that someone put some water pump lubricant in the radiator not realizing the cub does not have a water pump.

im losing oil from the oil pan

So are you sure it's going in radiator, or is it getting burned, or is it leaking past seals? More information please.

it comes out the overflow of the radiator

I'd say the block is cracked, allowing oil from the galleys into the water jacket.
How is the oil pressure?

Raymond's on the right track, there is a serious problem in that engine somewhere, if oil is getting into the radiator. It needs to be located and assessed for options, but a replacement block is likely the route you need to go. Best of Luck.

I've only had to deal with 1 cracked cub block in the cylinders and one blown head gasket, but in those cases the radiator fluid got in the oil, not oil in the radiator fluid. Something sounds odd with this.

Is oil actually coming out of the overflow tube of the radiator? Or is it possible that the oil is leaking from somewhere and then blown around by the fan and just looks like it may be coming from the overflow tube?

Consider draining both the oil and the radiator fluid to see what is actually in both of the drain pans. Depending upon when the oil and radiator fluid were last changed you may get a lot of gunk out of both places. A compression test may also be of value.

Todd

there have been only a few instances where I have seen oil show up in the cooling system. One was where the cylinder had a casting flaw where there were some pin holes in the cylinder. The other two were where the cylinder has a crack that ran the length of the cylinder that only leaked when the engine was at oporating temp. Keep in mind that in the old days people would add some oil to the cooling system to help slow the corrosion from just plain water.