rebuild

rebuilding a 1981 300D. Having a problem inserting the helical shaft for the injection pump, where the shaft meets the oil pump gear. It came out ok, but wont go back in. Could i remove the oil pump and turn the gear with a screwdriver and feed the shaft this way. First time rebuiding a benz engine, rebuilt many american engines, high performanct too. Just need a little help here, any help would be greatley appreciated.