Jason
The O2-A was about 800 lbs heavier than its civilian brother the 337. The wings had 2 tanks in each wing. there was the addition of a 3rd spar in the wing and hard points to carry rocket launches and ordinance. There are 2 titanium runners on the underside of the fuselage to protect it in case of wheels up landings (combat damage). The rear alternator is belt driven,while the front is driven off the accesory portion of the engine. Most O2's have repaired bullet/shrapnel holes. Anyone with anything else.
The O2-A is a beast on one engine, especially with external stores. Single engine ceiling is about 2200 ft in my aircraft with full fuel,pax and a warm day. The O2-A had a smoke system on the rear engine to make it visible to the aircraft it was controlling. The elevator was the earlier 336 shorter chord version with some of the counterweights taken out to make the controls heavier. The Military pilots were more used to higher control pressures than civilian pilots.
Will add more as I remember. Go to
www.cessnawarbirds.com for more info. You can get a great book there on the O2-A and other Cessna aircraft. You can see my O2-A at
www.huey.org and
www.mapsairmuseum.org
Tom