[Kos-Mos]

Crown yes, port not needed.

I would go with the bull version, but you will also need barrel spacers. I rarely buy mine, usually using a layer of double sided tape and some electric tape over it (the double tape gives the little squish to stabilize yet not jam the barrel). It's easier to perfectly match the inner to the outer that way.

For the foam pieces, all you really need is a gauge to consistently make the rings. I use some insulation foam tube for the foam part and winter add-in soles for the rest.
Best I found is to make sure the insulation tube fits inside your outer. You might have to remove a strip on the length to let it fit. Also make sure that when in there, the hole is at least 12mm (you need some space around the BB). When that is done, rough cut some rings out of it of different thickness (from 3 to 8mm). Then you have to make the rings out of the soles... that is a bit tricky. I found some washers that fitted just perfect inside my barrel (not loose, but not jammed... I got lucky). You can also look for bottles or anything round to make the rings. Mark and cut. For the middle, you want the hole to be LARGER than the one in your foam spacers. That is to let air (and sound) be trapped between the foam layers and not follow the BB.

You need just enough to fill the gap between the tip of your inner barrel and the outer barrel cap. When you have enough, stack them alternating foam/sole. Done.