I made this mistake... the ST150 carriers are a different size to standard Puma. Annoyingly at first glance they look identical.
When I did mine I got 2 2nd hand ST150 calipers - one came with the correct carrier and one didn't. I spent ages painting my standard carrier blue only to find it didn't fit... eejit.
Had to go and source a separate ST150 carrier and it was a bit steep at about £20 inc postage (well, I thought it was steep).
Maybe I was lucky, it was available on eBay, so check there first.