xr250 valve timing

i have an 82 honda xr 250r and the guy i got it from played around with the valve timing. I am trying to set it back to proper but im not sure which marks to use. On the left engine cover there is a plug to rempve and i see 4 different marks, one is marked with an "F" and one is marked with a "T" and the other 2 are not marked at all. On the cam gear there is one mark but where is it supposed to be? Up down sideways or what? There is also the possibility that the timing is 180 out, the 2 bolts that hold the cam gear to the cam fit both ways, so what is the easiest way to tell if that is right?