Wibhi,
The tail rotor started out on the left side, but in 1971 they began switching them over to the right. This negated the "running out of left pedal" at high power/high torque settings. On the left hand ones, the tail rotor rotated towards the nose of the aircraft and was a tractor-type rotor (pulled the tailboom to the left). With the switch to the right side, it rotated away from the nose and became a pusher-type rotor which was much more efficient. A very late-Vietnam Cobra MAY or may not have a right side tail rotor. Any subsequent model (P/Q/S/E/F) would have it on the right side.
As far as the Cobra Company cockpit sets, they are perfect for a Vietnam-era Cobra. There's a little scratcbuilding necessary if you want to add the 20mm cannon (there's an additional panel that needs to be added to the main control panel). If the references you have aren't matching, they may not be of a G model. Probably an S, which had significant internal changes (I just backdated a real front cockpit. LOTS of stuff to take out!)
With regard to the guns... the 20mm cannon under the left wing can be made with tubing. I did it once already and it looks really good. I just wanted something fairly simple to do it with and saw the M-163 with the Vulcan cannon and figured "why not!" its working out rather well. The ammo containers and feed mechanisms are all scratchbuilt, so its a bit of a conversion, but not too bad. I've basically built up the containers with laminated sheet styrene and then sanded them to the proper shape. Detailing from there is easy.
The minigun, however, is a royal pain in the butt. I've stolen miniguns from the 1/35 MRC UH-1C kits FIVE times now. (I have 4 G models building, one of em with twin miniguns in the turret) My poor Charlie models are all gunless!
I'm going to get some photos up soon of "Heather Dawn", the first one I've completed.