Help quieting exhaust (and why want to do that whats wrong with this guy)

[bogandoc]

Finishing a 5 year build of a RHD drive 33 hot rod with supercharged coyote 785hp.
Its fun but the exhaust is way too loud to pass regs here.

Rather than wreck up my perfectly good mufflers I bought some magnaflow XL 3 chamber turbo mufflers and have mangled them up.
Its possible after I pass inspection there may be the old mufflers going back in although that would be naughty.

Anyway they still aren't quiet enough, I need more baffling and/or flow restriction (yes, that hurts, but whats a few hp off 785 still batsh*t. assuming they will stay in the car of course).
Here are the innards of these 3 chamber mufflers. Arrows are direction of flow.

174745174746

I have a whole load of No 2/3 steel wool, I was going to pack the two outer chambers with that, and maybe tackweld some sort of perforated divider or something in that middle chamber so the wool doesn't just get blasted out the exit pipe.

I have no idea whether this is a dumb idea or not. I might go past a muffler shop and see whats in their recycling bin ask some advice but thought I'd post on here see if anybody knows their muffler design could advise.

Obviously don't want to over-limit flow and munt the engine. My first attempt at beer-can restrictors stalled the engine, and got blasted out the back of the car somehow, so that was a big fail.

[Nigel Allen]

I put 8 scourer pads in each sidepipe muffler on my roadster and got it down to 89 DB @ 3000rpm. At this level the cooling fan drowns out the exhaust.
I had tried lots of other alternatives but this was the only thing that really reduced the level without over restricting exhaust.

[J R Jones]

bogan,
Back in the day we were racing Nationals and Trans Am when "H" pipes were introduced. We found they changed the exhaust noise pitch and dropped the level somewhat. I have found "X" pipes do as well, a bit more effectively.

I ran a hotted-up Mazda RX7 rotary on the street and I remembered from racing days, nothing in the paddock was as loud as rotary's. SCCA tracks made then put slip-on mufflers on the tailpipe when not on the track.
With that in mind I went to the Mazda specialists for exhaust and they worked very well. They are also recommended for V8 applications, a pre-muffler and muffler.
https://mazdatrix.com/product/muffler-universal-rotor-shape-2-5/

Here is the weird part. When we went back to club racing recently the RX7s were still in GT3 and doing well. I asked how they were meeting noise specs these days. They had one large can that they cut open and filled with Lava Rocks (for BBQ). Through a season the violent rotary exhaust would pound the rocks to dust. When they got too noisy, they cut the can open and installed more rocks. Obviously there is some free-air space for flow.
https://www.acehardware.com/departments/outdoor-living/grills-and-smokers/charcoal/8005662?gclid=Cj0KCQiA37KbBhDgARIsAIzce1715Gk0XAzl 3zM-97uBoqvkLuphuhUHmlMc6pKxkfPwjTVKQL6l6QgaAiuAEALw_w cB&gclsrc=aw.ds

I would try them in your muffler in place of fiber.
jim