What state are you in and do they have an emissions testing program for diesels? Is the F250 currently a diesel?
From my experience, the people that work at emissions inspection stations are not the brightest people. As long as you don't have any big flashing neon CHEVY signs under the hood, I doubt that the inspection station would know the difference. But, if their inspection consists of plugging into the ODBII port and running a diagnostic check, then you might have a problem.
If you are converting from gas, then that changes things. I had to go through that headache, and if it wasn't for a glaring loophole in the WA state DMV system, then things would not have gone quite so smoothly for me.
1987 Jeep Grand Wagoneer...new 6.5 in process...diamond block, 18:1's, other goodies...