i need to know if the 2and1/2inch radiator replace the 1 inch on the f 250 1989 without any mods

 

Quite possibly, but if i remember right, the 2 1/2 inch radiator was for the v8s, and the outlet side of the radiator to the water pump is on the opposite side than our inline 6 water pumps... i put 2 lower hoses together with a piece of metal pipe to change sides on mine, but with such a massive radiator mine doesn't really warm up as well as it should.

It'd probably be worth your while to get the correct radiator, but i'm pretty sure the only mod you'd need to get you by is a longer lower hose

 

Or one can have a radiator shop modify the inlet/outlet positions.

 

unfortunately with plastic tanks, that is not an option