OK, as promised, a fuller explanation.
The boat is an Orion 70' trad, with the engine (a Beta 43) cocooned about 15' forward of the prop. The engine is tight against the left side of the hull at the foot of the bath!! (there are pictures on here somewhere but I can't link to them).
This leaves me with two serious problems 1, the drive is via a 3 part shaft with slightly excessive angles, causing wear and noise at high revs 2, more seriously, the starter motor is completely inaccessible (two mechanics have suggested the cheapest alternative, if it has to be replaced, is to cut a hole in the side).
So I am going to have the engine moved inboard (about 18") and forward about the same (thus shifting the gearbox from under a bulkhead and the bed).
The yard have suggested putting in an extra bulkhead to create an engine-room (fortunately there is a side-hatch in the right position). This would give better access and potentially, extra storage space.
So the bath (which we have never used except as a shower tray) has to go. To accommodate the re-positioned drive shaft the pump-out tank has to go so we will have to replace the toilet with a cassette or more likely, a composter (the tug deck includes an enormous locker which can accommodate waste while it continues to compost).
It's going to be ridiculously expensive but I don't see that I have an alternative.