I don't know whether the factory RGS goldie mufflers twittered
Mine don't and it's almost RGS engine spec.
I was told by a Goldie owner the twitter is down to valve overlap on the single, doesn't appear the same on a twin
Funny you should mention that but a mate of mine with a Goldie didn't have the twitter but his Royal Oilfield fitted with a Goldie silencer did. He swopped them over and now his Goldie twitters and his RE doesn't. There's clearly more to it than just valve overlap it seems.
We investigated, as you do, and found differences with the internals between the two silencers. They both had the perforated tube running offset down the side taper but varied at the exhaust end of the tube. We can't recall where the one that twitters came from.
One of my RGS silencers, the one from Cake Street Classics, has a perforated short tube concentric with the silencer bore which doesn't reach the end of the body as far as the two just mentioned and another I've just tried on the RGS has a perforated tube running centrally right to the end. Neither of these has any hint of a twitter.
That's 4 different internals for a start. I'll start a topic in 'technical' to see if anyone knows who sells Goldie silencers which twitter.
Alan