Your immigration status can be reviewed by the INS if you are physically out of the country for more than
6 months continuously. If you are gone for more than 1 year
continuously then you could lose the status completely if you don't have a re-entry permit.
There is no minimum presence requirement to maintain the greencard, so I am not sure what you are talking about in regards to the 160 days. But like the fellow before me said, it is only a concern if you are applying for citizenship.
Filing for the income exclusion is not an issue with the IRS. Just don't check the box at the beginning of the forms that say filing as a NON resident. There is a huge difference between being a NON resident and being a bonofide resident for the income exclusion.
Read the relevant sections in the immigration regulations. Follow the links at
www.INS.gov
With something as serious as this, don't take advice from a web board. I talked with 2 different immigration lawyers in 2 different regions before I accepted my current job.
I have been in a similar situation for several years. Never a problem, but I do own a house, etc, in the USA.