Problem solved and the credit goes to Anton.

This 601 has a single trigger. It won't move forward. The solution is to replace the right lock first and use a drift pin to push that spring loaded part back. [I did try a wire.]The lock will then go partly into place. Then move the cocking lever up and the lock moves completely into the stock. The left lock is not impeded by that unnamed spring loaded part and drops into place when its cocking lever is moved up.

Thank you all for your help.

danc