Thanks Howie. Sounds like you're set. I think it's in theory possible to apply for extension if you're going to be gone for more than year, but if you're found to have spent less than 2 years in the last 4 in the US, you'd lose it regardless.
Reentry Permits
Reentry permits are for people who hold green cards and know in advance that they must be outside the United States for more than one year. Under such circumstances, USCIS can allow you to stay away for up to two years. You should send in your application before leaving. Use Form I-131, available on the USCIS website at http://www.uscis.gov . If approved, a reentry permit will be issued and will serve as an entry document when you are ready to return.
Too bad no such thing as IRRV for US. I like to keep my options open. :-)