Do you have $80,000 to burn? You will appreciate the FAA after you read below.
Iím involved in converting an FAA Comm and Inst to the UK JAA ATPL(H).
You need to go through an ATPL ground school, either distance or in person. The amount of hours needed for conversion are spelled out and it looks like 30 for the Comm, 9 for a turbine transition (AS355) and 40 for the Instrument. One schoolís approach for the IR is to fly 25 hours in an R22 and 15 in the AS355. In the UK you need a real IR machine for the IR test.
On the upside, the UK ATPL(H) is valid through out EU nations and is accepted in many other nations. With the declining value of the dollar and tax free status of other countries it may sense to go for it.
You can easily get into a distance learning course, but be prepared, itís tough. You will learn things 99% of American ATPís are clueless about.
Also, look into Helicopter Adventures as they are running a JAA program, you might be able to do the Comm part on FL.
PS Ė learn to drink warm beer!!!