Complex sentence: The original airborne receiver unit was AN/APN-4 unit of 1943, it was largely identical to the UK's two-piece Gee set, and could be easily interchanged with these units.
Split into simpler sentences: The original airborne receiver unit was AN/APN-4 unit of 1943. It was physically identical to the UK's two-piece Gee set, and could be easily interchanged with these units.