zf5 is a pretty easy swap. The truck is not intercooled, the intake hat your friend is refering to is from the ATS kit and the kit isnt intercooled. An intercooler kit will change that piece out obviously, as you would need to run the hot compressed air from the turbo through the intercooler THEN back into the intake manifold, your engine bay is absent of intercooler piping, the intake hat required for intercooler piping, and (I am just assuming this I have only laid eyes on a customers OBS powerstroke with an intercooler kit) a reclocked turbocharger intake housing, to allow for the corresponding intercooler piping.
I would also hesitate to claim the C6 is built because of the previous owner claming that an intercooler kit was on the truck. That is not to say that it isn't though, as this is one of those, the absence of evidence is not the evidence of absences type situations, or however that saying may go if I am typing it incorrectly
2nd time saying this, still a nice truck, I paid 1300 for mine, another 300 in tow fees and then 800 for my ATS 093 factory kit locally, so all and all my 1984 F250 XLT extended cab long bed 2wd truck has cost me 2400, so do the math on your truck vs mine, I don't think the extra inches in the cab is worth 1400 dollars.