Sold payment pending. Sorry david, not sure if they would fit a 120y. If you start a thread im sure there would be somebody who has been there and done it. I sent you a PM.
Im running a g13b in my 1000. I used a sierra box and yes they are large compared to 1000 box. Even if you could bolt a cappucccino box on to a g13b, I don't think it would last 5 seconds and there not the type of spare part you can keep a stock pile in the shed.
If you can get past the tunnel mod, put a g13b in it. G13B ticks all of your boxes, one more than the cappuccino. I think a cappuccino weighs a little less than a 1000 and you have to ask yourself, Do I want to spend all that money and time for a 17 second, 3 cylinder car? Another thing is that a 1000 tunnel is tiny dude. You could hunt around and purchase a cappuccino motor and box and still end up doing a tunnel mod.
If you can't get past cutting you car then just go A15, it will be so much quicker and also ticks all your boxes. You could always fit EFi if thats what your after.
Good luck anyways and if your heart is set on a cappuccino engine then have a crack. It would still be cool.