Hi There and welcome to Chevy Chatter II. Glad to have you with us!
On your distributor moving around, it could be caused by either a bent shaft in the distributor or the distributor might not be down against the engine block as it should be thus the distributor gear is not engaging the cam gear correctly. By the way, there is no bushing in the block for the distributor.
Also, just for future reference, when you post again you might want to post in the 1937-42 forum instead of here in the 1912-1928 forum. That way more dudes that are into your model year will read your post and they can help you with any questions that you might have.
Good luck with your 1940 cabriolet.