Youve found the one difficult nut then
You will be needin one of two things to get to it.. Either a flexible socket extension which your sposed to be able to get from halfrauds but i could never find one or a small universal jointed 14mm (if memory serves correct) socket. I went for the latter and could just get onto the nut to undo it. Its a right fidley thing to get at but patience is the way
Have you managed to get the turbo oil feed bolt out of the block yet..?? I would imagine not of you still have the manifold on.!! Thats another tart of a thing to get at. Highly recomend a ratchet spanner for that one
17mm i think. Then look at gettin a braided turbo oil feed as its much easier to get back on than the solid pipes..
Good luck wiv it
J..