I merely posted the link to the two bbl set in Morphy's auction. He posted a PGCA letter that states 2 3/4" chambers. I'm sure Chuck copied the information as he saw it in the records. I don't assert they are or are not 2 3/4".
My 30" gun was commissioned and upgraded by Delgrego and Runge for Sheldon Gitman around 1979. It was originally built in Meriden, as a VHE with 30" bbls, straight stock, and single trigger. I don't know what the chamber length is, but only load 2 1/2" in 28ga, so I don't really care.

The 1929 vintage "Chamber 2 3/4-inch" most likely would in theory be for 2 7/8-inch shells.

That is quite the Frankengun!! Five Remington repair codes on one set of barrels. Stock work looks more Remington than Parker Bros. to my eyes. Was one of the original 30-inch barrels whacked to 26-inch? Or, is that a new set of barrels added at a later time? No mention of beavertails, checkered butt or SST in the letter.

It's been dolled up a fair bit but is still a valuable gun, not the least of the reason being it is the only 30" 28ga. CH grade ever made.
The listing, while somewhat inaccurate, opens up more questions than answers them. It isn't listed as having BTFEs, but one of the barrels has a reinforced fore end loop, and the other does not. Also, one of the fore ends has a correct iron for BTFE, and the other does not.
I suspect one of the 30" barrels is now the 26", looking at the chokes. Original full chokes were stupid tight, so bobbing 4" could still leave them with IC, as the listing states. The gold work, not Parker, isn't the worst I've seen but ought to be removed.
Mr Gitman was known to commission several A1S upgrades, and My suspicion is he chose to upgrade mine to CHE may be because there was only one gun ever made with those characteristics. Apart from Runge's signature, it is a faithful likeness in all respects.