for some reason, the malossi belt for ciao is too long. i think it's because the variated ciaos in europe have larger rear pully cheeks than our lowly american ones do.
i got around this by extending the motor mount slots forward probably a quarter inch. if you do this, remember there are 5 holes total.
as for the rear cheek hitting, you need to add an extra washer or two behind the variator plate to space it out some. the larger cheek doesn't fit as well as a stock variator. i've also taken a large punch and a hammer and flattened out the rolled part of the frame some to help clear.
if you're having this issue, you probably know what i mean by "rolled part of the frame."
as isaac said, there's a plate rivited over the rear hole on (i think) every vespa frame, EXCEPT the ciao. behind it there's the long slot you need for adjustment.
when i find a new frame to replace ciaociao's twisted one (if i ever find one..) i'll actually document all the frame mods to make things fit/go on easier. i should have the first time around, but i didn't think about it apparently.