Not really. Unless you can mill the spacer to be thinner. I would hate to alter an old school relic like these. I’m not sure how the loading lever is assembled in there either. You would need to examine that pretty close. Not much info available for these anywhere either.
It's pretty easy - follow their rules. Allow 5 -10 extra minutes for check in. Pistol cases go into your checked luggage. Rifle/shotgun cases will be in baggage claim where large items like golf clubs come out. Sometimes confusing at smaller airports. Use good locks. I've done this often & never...