Can I use the same fitting on my radiator for the overflow can to attach the cylinder head steam line? I was thinking of adding a "T" there.

 

Nope it needs to be plumed in the pressurized side of the cooling system. You'll either need to add a nipple to your radiator or put s junction in one of your radiator hoses to route it to.

 

No, if you T into the line between the radiator and overflow tank the steam line from the cylinder head will be on the wrong side of the radiator cap. The steam line needs to go into the low pressure side of the cooling system, but if you put it into the overflow tank the cooling system will no longer be a pressurized system and you will just fill the overflow tank with coolant. Either run the line into the low pressure side of the radiator, T it into the return line from the heatercore, or drill and tap the top of the waterpump and put it in there. If you do a search you can find pics of all 3 solutions.

 

I just drilled and tapped a hole in my radiator and ran a -4an line to the vent tube. The connection coming from the vent tube you can't see in this picture but you get the idea. Seems to be working fine:

 

Thanks for the help. I'll plumb it into the low pressure side.