IMO, you and the gun will both be happiest if you stick to light shot charge shells of known low pressure. Note that USA modern 2 3/4" shells are to SAAMI standards and will be of relatively high pressure. Opening the chambers to 2 3/4" does little to nothing useful for you. you want low pressure for the metal and low recoil for you and the wood parts.
A 250 unit bulk box of Polywad Vintagers will run in the $90 region on your doorstep. "Cheaper" can be had by handloading 2 3/4" cases to known/published data with low pressure and light shot charges.
