the best way i could say with any motor is if you don't mind takin 1 valve cover off or maybe you can peak down the oil fill of the valve cover to see the #1 intake an exhaust rocker arms. but what you want to do since your motor is together is turn the engine over (by hand) until you see the #1 cylinder intake rocker arm move then line up your timing marks to 0 TDC right after #1 intake valve closes an drop in the distributor with the rotor pointing to #1

or otherwise you could gamble with it if you don't want to pull off a valve cover an play a guessing game an just line up the timing marks to 0 TDC an drop it in an if it don't run an shoots flames out your carb your 180 out an need to lift up the distributor an turn the rotor a full half turn an drop it back in an be right. if you get flames out the carb (sparks when intake valves are open) try retarding the timing an if it backfires out the exhaust (sparks when exhaust valves are open) try advancing the timing to see if it'll run and if not your 180 out. an start over its alot easier to look an watch your #1 rocker arms