The Italian Group JTD engines, as licensed to GM, may have the same blocks, but I think you'll find that the heads of these engines (and more particularly the cam profiles) would be different from say, an Alfa JTDm, and the same block found in a Vauxhall.
Following on from this I would presume that the cams would need to be locked when changing the belt? You certainly need to do this on the petrols, but on the diesels this may also be necessary - in which case the garage would need the correct cam locking tools to do the job properly.
Personally, I would take it to a good Alfa specialist who is familiar with these engines. I wouldn't take it to a 'general' garage round the corner. The specialist may be a little bit more expensive, but hopefully they'll do the job properly. There is nothing worse than a cambelt job being botched - you'll regret it bitterly if this ever happens to your 147.
Finally, when you get the cambelt/tensioner/idler done, change the waterpump as well. Take a look at the sticky thread on 'JTD waterpump/cambelt failure' on here if you need to know why. Again this is more of a reason to use a specialist, as most will change the pump without additional labour - something a 'general garage' will be very unlikely to do.
Last edited by Spider95; 12-07-09 at 18:57.