We've made some progress - It was possible to get that lower timing belt cover off with head still untouched. Next step still tricky but we have a plan !
Our problem is that the plastic timing chain guide (on the opposite side from the tensioner) which should be held on by two studs has come loose. Amazingly the plastic guide is intact but the two metal studs have sheared off. Removing the plastic guide doesnt appear possible without removing the head as it protrudes up about an inch into the head and although we could break it to remove it there's no way to get a new guide in place in one piece.
Our plan is to remove the remains of the metal studs (done), bring them to a machine shop, drill a hole in the top of each get cut a thread in this hole so that we can screw in fresh bolts to hold the guide in place.
All sounds a little unclear in text, but, basically there's hope that all can be done with head in place !