[rotorwrench]

I'm not real well versed in the Ford 250 I6 information. I can't even find what type of rocker set up they have but I suspect they have the full rocker arm shaft set up. The older ones up through the 170 had adjustable rocker arm set up but that started to change in the later 200 configuration. Some were adjustable and some were fixed. The fixed type would require the push rods to be changed if the head was milled. There is also a problem getting the old thin steel head gaskets. If the gaskets are composition then it adds a lot of thickness that will change the valve clearance properties and the clearance volume unless the head is milled to compensate for that.

If it happens to have separate adjustable rockers then it should adjust for proper lash or there may be different length push rods to compensate for irregularities like I mentioned previously. I don't have a shop manual so this is about all I can offer on possibilities for this engine.