Here is the Screamer Silencer I built just before I pulled my RST apart. It is 38mm and was made to run alongside a 3" exhaust. The outside diameter of the silencer is about 3".

The flange is a normal Tial flange, you obviously run a Screamer pipe down and under the car, then make the join to this Silencer, I planned it so that you could remove the Silencer and run the Screamer unsilenced if you wanted. It's like new, as it did one run to Brunters. It takes pretty much all the noise of the External Wastegate, it worked really well.

I'm after £80 for it.