I did it a few years back. I validated my CPL and MECIR at the local FSDO which allowed me to fly anything on my CASA CPL licence in the US. I then sat the IF initial written exam (was originally told to sit the foreign conversion but FAA was not sure so ended up sitting both) and did a IR check ride in a 172. Very easy - they let you use anything the plane has such as moving map Garmins. I then did the CPL written. Then a CPL check ride in a C310 which included an IR "add on". To fly commercially in the US you have to do a CPL check ride. This was the most cost effective way but I do not have a FAA CPL single engine. The "add on" portion of the check ride for the multi IR was 1 single engine ILS approach. Overall, very easy.
Hope that helps.