I don't remember but it came out on my 84SD. It looks like the head takes an allen wrench. If so, try cutting up a right angled allen wrench and tapping the long leg into the bolt. (Tapping helps seat the allen head wrench. You reallllly don't want to strip it.) Use a socket on the other end to turn it. I have a few metric allen sockets but also several legs of various lengths and size that I use when I don't want to grind on a socket.

I do remember that this wasn't on my list of favorite jobs. You may want to consider some of the cautions in this thread when you do get the bolt out.

http://www.peachparts.com/shopforum/diesel-discussion/328295-leak-free-617-a.html

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.