Do you have an open end or closed end cap?

 

What do you mean open or closed?

 

My wife and I both have these mufflers and I don't recognize that end on your disc stack with the threads sticking out. Are your mufflers 3" diameter? I poked around online and found this info.

This is the open end cap for the disc stack

https://www.ebay.com/itm/SuperTrapp-...cAAOSwk5tcnvPs

This is the closed end disc cap looks like this - these are for 4" diameter, the 3" looks the same.

https://www.ebay.com/itm/End-cap-clo...sAAOSwOhda24Nn

Here's a view of a new dual muffler kit with tapered end caps. The disc set on this has the closed end cap on the far left of the lines of discs in the second pic. I don't believe the piece on the disc stack in your pic was part of the original configuration.

https://www.partsgiant.com/p343674-s...lip-on-exhaust

 

Cannot help with the mufflers, but Your bike sure looks good!

 

It looks like his mufflers have only a center screw to attach the discs. Which is way different than the three sockethead machine screws that were used on my SuperTrapp slipons.

When I autopsied the SuperTrapp slip-ons I had on my FLHS, a shop must have installed one open ended cap, as the other was still the closed one I had installed on both mufflers. I later found out, that the open end cap allows them to insert the A/F probe into the muffler when tuning the bike on a dyno. They must have forgotten to remove and replace it...