How do you think that he will do that...?
Because he has to convert his ICAO CPL-H to FAA CPL-H, and he will do that. But how to convert IR when his ICAO licence is without that IR-H?
It is very relevant for him because without IR-H he won't be able to make FAA ATPL-H licence!
He will have to do full IFR training, 50 h of flight training for IR-H. And that small thing completly change the whole situation.
He should ask some FAA flight school how many of military instrument flight hours (without civil licence) they can accept (if any) for making IR-H. That is first step.
It's no so simple as you said...
JR