I have a 1949 chevy 3100 truck I am restoring but am having an issue with the parking brake adjustment.

I am having a problem adjusting the parking brake as the 1949 chevy truck parking brake lever extension (this fits between the two brake shoes) seems to be too long as the brakes are locked up when the brake shoes are adjusted as far in as possible with the parking brake lever extension installed. The brakes work fine without the parking brake lever extension installed.

Has anyone had this problem or can point out what I’ve done wrong?