You really should look into the regulations...
For type ratings on single engines, you need (if i remember correctly) 100 hours, for multi engines 350 hours (or was it 150 and 300?).
Regs state you need to have a valid rating-as ut refers to ICAO licenses, which the FAA is clearly not...
For each "conversion" a letter has to be sent to the CAA by an ATO, requesting permission....
So in your case:
If you have the minimum hours required, an ATO can issue a letter for the CAA saying "no further training required"-and the CAA can then approve a checkride, as they know that there are no ratings under 12500 lbs for FAA certificate holders.
Its complete bollocks, i know...flying helicopters in EASA is not fun any more....