All the Lefever guns I've had any dealings with have had a long taper choke, running to about 4" in full. For lesser choke the taper gets shorter. It would at least appear as if all the different chokes could be cut with the same reamer depending on how deep it was run. If I ever encounter a Lefever with a muzzle parallel I will assume it has been opened.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra