Post boil I ended up with about 7L at 1099! I did some back of an envelope calculations, boiled up some extract in water and added some additional water which brought us to about 1073 (from memory) and just shy of 15L.
Fermentation, with T-58 was rapid for the first couple of days. It got down to 1030. Checked it today after a full week in primary and it's still at 1028, so I've roused with a sanitised spoon.