@Humpleupagus @1iceloops123 There were two tabs of plastic blocking the Japanese carts. You could remove those tabs, or you could take a dremel tool and grind notches into the Super Famicom cartridge and they would just work. I preferred to grind the carts so I could take them to friends' houses to play on unmodified systems.

The reverse, playing American carts on a Japanese Super Famicom, always required an extender because American carts are wider than Japanese carts.