Why alter the original configuration of your gun now when firing 2 3/4" shells hasn't hurt anything up to this point? Actually, your greatest risk is probably the likelihood of cracking the nearly 90 year old wood when firing the "heavies" you mentioned. Opening up the chambers 3/16" isn't going to do much, if anything to reduce the potentially stock damaging recoil from heavy loads. Stick to the lighter loads, and use the money you'd otherwise spend on gunsmithing work to purchase low pressure 2 9/16" loads.
