IC choke on an English gun was generally around 0.006" constriction, even ¼ choke was only about 0.010" constriction. Since these are given as diameters only 0.003"-0.005" is removed from the actual wall thickness. "IF" there was ample wall thickness it would have been no big deal to have reamed the barrel a bit oversize leaving an IC choke at the muzzle.

I would not really see anything to arouse my suspicions it was re-barreled rather than just re-bored & re-proofed.
I Didn't Say Everything I Said, Yogi Berra