Bruce,
Jack up the back of the car and turn the tire. If the other side turns in the same direction = posi. If it's still functioning.
Neat sticker on the frame, I've never seen that.
I also have a 3:36 posi, Fremont car, but didn't have the "LF" mark on the bottom of the axle housing.
I notice yours has the green stripes on the axle tubes.
3:36 was the standard 4 speed rear ratio.
Mark