I used to use a Lowrance GPS200 in the C130 (coupled to a Psion 5 running Sierra flight planning software) before we got GPS/IRS installed, and it quite happily coped - and this was sold as a fisherman's navaid in deepest Northern Canada. In fact, it was a bloody good combination, with all the functionality of a Litton 92 or FMS (without VNAV), for far less than the cost of your average aviation Garmin.