I have seen Chris' concertina, I am a "newbie" and didn't realise that some Maccanns started on 'C'. I have a New Model 55 key, with all leather bellows. I have a bit of frustration trying to play tunes without going up an octave, (although I should be used to this as I play recorder, mainly soprano). I sing soprano, so wanted to be at the same pitch. I spent an entertaining couple of hours trying to work out if you could move the keys around on a cheap 46 key (might need a few extras) to get the same effect. Nothing came of that, I don't know how the fingering would work!
I did consider buying Chris's concertina, but can't really afford it. I also considered asking him for a part exchange, but I don't want to part with the New Model I have, partly because it was given to me by my father in law and it's a very nice instrument. He gave us 2 Maccanns, the other was a 46 key with brass reeds and rosewood ends which I tidied up and husband Brian repolished. We sold it on to finance the refurbishment and tuning of the better one by Andrew Norman.
For those interested the numbers are 789 for the 46 key and 805 for the 55 key. Father in law's first wife's mother(!!) was an accomplished piano player, so may have had these in succession.
I have looked at this topic on several occasions, so have totted up some of the 734 views!