From Ad;
"Original 28 barrels which have recently been reproved, with 2 3/4 chambers and are choked 1/4 and 3/4."
This would indicate it was reproved after the chamber lengthening. Of course would be good to make certain this is true. I am not certain on reproof but original proof was normally 1 1/8 oz for a 2" chamber & 1 oz for a 2 3/4" chamber.

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