I am also in the process of rebuilding my CT26. The nut you are refering to can be taken off with a 3/8 socket. You just have to tap it on there lightly. My turbo rebuild kit came with a new nut. Here is a link to a website that has some great pictures that may be of some help.
http://www.mybluemr2.co.uk/CT26/index.htm
He is the one that suggests the 3/8 socket