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A PT-48 would work well.

Agreed on the big bowl mouthpiece. If I can remember, I'll get the marks off of the mouthpiece I use and reply to this thread.
Definitely not a funnel (Helleberg) shape.

Edit - The mouthpiece I use is stamped 'B. TILZ - NEA' at the top of the bowl and 'M0' near the shank. It works very well with this instrument.

Edit 2 - I found the specs online for the Bruno Tilz NEA 310 M0 mouthpiece https://www.mundstueckbau-tilz.de/310-b-tilz-nea.html, and they match what I see.
Huge throat, Large diameter at the rim, Deep cup. The contour is more of a bowl than the Conn Helleberg 120S that I have. It's honestly not a good mouthpiece on any other instrument that I've tried it on, but it works very well for some reason on the Mack 210.

I used a Bach 12 with success but found the TU25 I use now more comfortable throughout my practice.

It also imparts a more organ-like tone than an Oompah like tone.

The RT-50 was just too big for me.

The RT-48 could be worth a try...

I've got a 210 and both the Kanstul and Blessing 18's rock out on it. I've also had luck with a Houser/Sellmansberger solo cup with a Hellberg Modified rim, but it is a beast across the board, high to low with the 18's. I was originally a Schilke guy (and, not downplaying their quality) tried my old Schilke Hellberg, Hellberg II, 66, and 62 on it (as well as some other well known brands), and none could touch what I could do on it with the Kanstul and Blessing 18.

Mark Finley wrote:Maybe I should do a short demo video.

Sounds like a plan!