ducmarc,
I had a friend who had one of these over and under shotguns that he wanted to sell me. I had considered buying it to convert to a rifle but rejected the idea because of the lockup on the gun. I honestly don't remember what it has for a lock up but I know at the time I didn't think it was fit to convert to a rifle. If your gun has a malleable iron frame on it, that to me would disqualify it for any kind of conversion, in my humble opinion.

I would suggest you enjoy it as a shotgun and find something different to convert to a rifle. Both calibers you mentioned are way too high in pressure to even think about putting into a conversion gun like yours. The .405 is about at the top of the pressure list as far as what can be done, and that needs to have a good tight donor gun with double under lugs and a third fastener on a hardened steel frame. Anything less and you may be wearing certain parts of your gun for life. Sorry to rain on your parade but I would rather disappoint you now than to have you get hurt or worse. Bob