In short, 500 is spot-on...

I see that you're in Brazil and a phone conversation may be tough, but if i were you I would get in touch with either.

JJ Perodeau at Champlin Firearms (Liege Trained Gunsmith)
www.champlinarms.com

or Kirk Merrington (English Trained Gunsmith) he has a website somewhere... do a search for it.

They are two guys i know that can build a set of Double Rifle Barrels.... (From scratch - if need be.)

They can tell you immediately whether or not that action would be suitable and for what chamberings.

I've had this conversation with both of them... and believe that they will also tell you what they've told me

"if the action came off of a double rifle, then it is suitable for another DR. - if not it's a gamble with your money, and they will make no guarantees" (assuming they take the project on)

"If the action came off of a shotgun, then it it not suitable."

Despite their visible similarities, there are apparently many differences (in thier opinions) between SG actions and rifle actions.

If it were a MERKEL shotgun however... well, that would be a different story alltogether!!!

right, 500?