The injector nozzles are retained in an upper and lower part that screw together. As cimo says, a deep 30 mm for the upper part that retains the injectors but I found that in some cases this comes unscrewed whereas in others the whole lot comes out. If it all comes out as one you can use a vice to separate the two parts but in order to unscrew the lower part from the head you will need a 41 mm socket, probably only available as a 3/4" drive, so you need an adaptor to 1/2".
It so happens that I have all of these, now surplus to requirements, that I am prepared to sell at a very reasonable price. PM me if interested.