If you have TheB24Guy's OH P-39, then the _r is for the right side and the _t is for the left. His model has the de-mirrored textures and has the VC cockpit. It is a direct replacement for the stock P-39. Its actually made from the stock model so everything lines up.
If you can't find the model here then you can get it at SOH...http://www.sim-outhouse.com/sohforums/l ... 52&id=5874
Allen Doweny has also made a few other versions of the P-39.