I wouldn't think that there should be any issues. I had a GTN650 working with my 4500s before I upgraded to 5500s. The GTN series is for the most part work the same across the line. (except for the obvious feature differences) All the GPS steering data comes over ARINC. The obvious thing is due to the lack of NAV source, you're limited to GPS approaches only. (unless you have another NAV source)