Yep 19mm...OR!!!! 1/2 inch bolt head
If you have a welder and some goodies handy you can make yourself a really nice allen wrench setup

I cheated and used some pretty serious heat (and force) to get it out though.

Also...don't use the pipe wrench. Only about 1/16-1/8th inch of plug stucks out..and its rounded..
I think attacking the edge with a pipe wrench would just reak havock on the plug.
Also it would be nearly impossible as you would ahve to right parallel with the side of the block to get a good bite.

I'd go with the head/cold myself
And just so you know
on a turbo engine
it sure looks a LOT easier to pull the manifolds/turbo setup than pull the starter and still not have enough room..
espically if you plan on using some fire
:fork_off: