Circa 1921 12 gauge VH 2 1/2" chambers ?
 

Would this have still been the norm in 1921 to have 2 1/2" chambers in a 12 gauge gun ?

More likely 2 5/8" for 2 3/4" shells.

12-gauge 2 5/8 inch shells were still quite common in North America upto WW-II. So, a customer might order a light 12-gauge specifically for the 2 5/8 inch shells, which with Parker Bros. policy of holding the chamber about 1/8 inch shorter than the intended cartridge, would give a 2 1/2 inch chamber.

I don't know about the Parker records, but I have noted the occasional 12-gauge Ansley H. Fox ordered chambered for the 2 5/8 inch shell. To date
I haven't come across one of these guns ordered for the 2 5/8 inch shell to measure the chambers.

Well if a chamber gauge is any indication this thing at the moment is 2 1/2" .

If your gun is listed in the Serialization Book, stock book entries for chamber length may be available in a PGCA letter.