I converted one of these to a fermenter many years ago. I pulled the guts out of it, then strapped it horizontally to a little flat bed cart. I bunged the side (serving port) and use what was the side port as the filling and transferring hole (w/ large bung and airlock).
I didn't serve out of it, and it was kind of a pain to clean. I decided to keep it amply supplied with brett and oak cubes for aging, and just kept topping it off with fresh wort when the time was right.
Life happened, so I don't use it much these days, but it was a lot of fun!