TubeNet

I had a gig at Great America in Santa Clara that required me to play euph & alto. I had a Mirafone 1 1/2 G that I used in the euph (Yamaha 321), and I had a Mirafone 51D copy that I used in the Mirafone contralto. Dick Ackright shaved down the 51D mouthpiece to fit into the alto shank. It worked just fine, FOR ME. I had a GREAT time on this gig and enjoyed playing a part other than the tuba parts.

If I had to play 'real' music in a serious concert setting, I would defer to a musician who actually studied horn and played the instrument on a regular basis. Playing at an amusement park, silly arrangements and transcriptions, for an audience that didn't even know we were there, I am SURE my performance was acceptable.

Denis Wick 2 is on the large side at 19mm, and it's a popular choice if you're shopping for a mouthpiece. Too small for you? Who knows, I think might be better to give it a try with a normal mouthpiece first? I have actually played in public on a DW 2 with a couple days' practice (though admittedly to the lowest possible musical standard!)

Shank size is a little smaller than small shank trombone. There's a slight chance of confusion between alto horn and mellophone. The latter has a significantly smaller shank, but I assume you will steer clear of the mellophones (not that I have anything against them, I guess that's just where I'd draw the line on the tuba family - alto horn maybe, mellophone maybe not.)