Useful tool and method for accurately positioning the engine at TDC in this link.
http://www.pembleton.co.uk/ePAG/ePAG30/MGtiming.html
Ignore reference to cylinder 2, this info came from a moto guzzi site (90 degree v twin).
If you measure the distance around your pulley circumference you should be able to work out the number of degrees they are apart and be able to decide which one is TDC (0 degrees) and which is 6, 8, 10, etc. My guess is that no.3 is the TDC one and that 2 and 1 are two out of the 6 to 14 series.
My scimitar handbook lists 10 BTDC as the static setting (or running at slow idle with vacuum pipe disconnected) for 97 octane petrol but you may need to retard the ignition to cope with 95 unleaded.