The JTDm includes an 8v 120bhp version and a 16v 150bhp (post facelift) 16v DOHC version. However, the JTDm 8v never made it to the UK - all JTDm engines for UK spec cars are 16v.
http://picnic.ciao.com/uk/8582742.jpg
http://pictures.autotrader.co.uk/img...a?id=679469910
All are common rail direct injection diesel engines but the JTDm (red m-jet badge on the rear boot lid, and in the case of the 16v, additional 16v letters on rear boot lid and engine cover - see above picture) has uprated injectors which operate at a higher pressure than those in the earlier non-m JTD. The 8v JTDm engines never reached the UK though.
Spot on, the "m" just means revised injectors over the "m-jet" cars-But perhaps you better let Alfa know that the (sohc) 8 valve m jets never made it here, as their website and brochures say they re on sale now and have been since the facelift!