I've been talking with Legacy Sports International (the importers into the States for the Puma rifles) and they are telling me that they have been installing the XS Ghost Ring sights on a couple of these rifles and finding that they are working out great.
When I was at reliable last week Shane had the XS sights and the 16" rifle in stock so I popped the rear ghost ring sight on to see how the sight worked.
If you wanted to install the sight behind the lugs you would have to remove the safety or you could mount it just in front of the lugs and still retain the safety.
I would definately recommend the XS Sights on these rifles.