RSTs should be fine pressure wise if the gunsmith gives the OK. Recoil is another matter. A one ounce shot load will recoil about 1/7th harder than a 7/8 oz shot load at the same velocity and will put 1/7th more stress on the head of the stock. If your gun weighs six pounds that might make a difference. If it weighs eight pounds, less so. How heavy is the gun?

Hodgson publishes recipes for 7/8 and even 3/4 oz 12 ga loads, if you load cartridges.

Nice gun. Have fun!