New tank on order so hopefully all put back soon.
Neil, you will lose some coolant. Unavoidable. It will drop to the heat exchanger level. No problem, except the mess. Just top it up when refitting. Above the coolant tube on the exhaust riser is a brass plug. Open that when refilling to remove the airlock, or better yet take it out and put it where the barb to the header tank hose is - swap them around to avoid airlocks in future.
IT, when I come to plumb back in what should I use to top up the engine coolant? I was thinking just plain old de-mineralised water same as I'd top a battery up? Or is there something else I need such as a corrosion inhibitor? Plenty of coolant still in there so only a top up really.