I haven`t done plugs on these so couldn`t say what they are like to do,there are some awkward and difficult glow plugs out there and sometimes a lot of ancilliaries need removing to gain access and be careful when removing as it is common to get seized plugs into heads and snapping off, usually meaning a head off job. A lot of glow plugs nowadays work on 4-5 volts so testing them across a battery can burn them out and an ohmmeter would be the way to go to test each plug individually and safely,if you do get them out it is usually quite noticeable if one isn`t working as it will be a different colour to the rest,good luck.
cdc, June 2015