call your tinners, and they'll tell you.
you will be able to move your furnace as far as the trunk line section that it is tied into now extends. as you look at the trunk line, you will see the biggest size supply and return duct directly above the furnace. to move the furnace further than this section, you will have to totally rmove and reinstall new trunkline to accomodate the airflow of the furnace.
As inspector d said, you will also be limeted to the length of the flue according to the manufacturers specs and local code.