Thanks for the comments, everyone!
I like the 'drop in' idea, so it can go back to being a Carrochio at will, or if there is a crane around.
My older steam tank (the one that's half war wagon and half tank) does the same thing - it can switch between volley gun, steam gun and mortar. Not that there's any point in that now.
Less excitingly, outriders:
Now I need to find the other ones. I should have four more somewhere.
Still not sure if I want to keep my owlbear knights, or if they look rubbish. I'm not too impressed by the models.