JR, be glad you're not in Europe looking for job with JAA/EASA licence.
Zlocko may not bother with European IR, as he can get job with his medium heavy twin PIC time with FAA ATP elsewhere.
Let me put this simple. FAA training - crediting of other ICAO IR training, minimum 15hrs with helicopter instrument instructor total, of which HAVE to be 3 in HELICOPTER previous 2 months before checkride. Most of training can be done in fixed wing, sim, etc. All relatively cheap.
Now try standalone JAA instrument rating. 50hrs of training, of which 10 or 15 have to be in actual aircraft - helicopter. For it to be of any (exceptions exist) use for twin offshore jobs for young CPL pilots, the sim would likely be at the cost exceeding R44 rental in the US. Now add in 8hrs minimum INITIAL TWIN rating. At 2000-3000 USD/hr. Before doing the IFR training. So you're looking at quite a lot.
UK examiner for CPL or IR? 1000 bucks to CAA thank you very much. License issue (admin fee, FAA free of charge) - 230 or so GBP.
Head not spinning yet? Try doing partial fail, retest at half the one grand USD rate, plus rental at that crazy price. Plus any IR theory or exams again if his IR credit expired. No such thing as easy FAA IR written. It's rather 7 separate IR exams that need lots of studying/cramming.
Sure, there's reduction of minimum training for heli IR if one has JAA airplane IR. Which Zlocko doesnt. Still more than converting ICAO IR to JAA IR.
That one for multi would be 10hrs minimum sim and 5hrs aircraft. Put extra 5 hours for second/third twin rating. Maybe in his case still 8, as he ain't got JAA licence rating, only S300. Think some CAAs can put the rating onto licence, if you ask nicely, subject to person having 500+ PIC time on those.
Oh, hang on, Croatian CAA won't give him licence. Or the neighbouring country probably not being nice to do so, else he'd probably already have it.
It's third of the cost, doing twin IR for Europe, from FAA IR. Actually, with FAA ATP, he can simply drop the whole Europe thing and get well paid cushy job in ME instead of flying Mi17 in various not very nice places.
He can do FAA validation to have PPL (after he gets current/legal), which he'd add the FAA IR (US test passed) to it, which will be used for FAA ATP ride. Voila. Job done.
Why all this? The cost, bureaucracy. USA is 'can do' for aviation and keeping it simple. Not so in Europe. It doesn't matter how he gets ICAO IR (Faa in this case) to convert into European one. BTW, he'd still pay in the region of 20-25k EUR for the cheapest way conversion to JAA/EASA IR(H) on twins.