I bought my 507B mine in 1984. I have moved several times and have not let go of this great stove. It has sadly been sitting in my basement waiting for the moment I would regain my sanity and start using it. I bought a Harmon Mk2 that I plan to use for the bulk of my heating this year, and since I am limited in number of flues, it won't be until early next year before I can get a chimney up for the Jotul. When I did burn it I used mostly nut, some pea early and late in the season It never occured to me to mix the two (a youthful lapse). This forum wasn't even an itch in someones pants so most of what I know about burning it was trial and error an it was very trying with a lot of errors. Once you have conquered the steep learning curve life will be good, very good.
Your 507 looks to be in pristine condition on the outside you can find parts for it, but as was mentioned they are steep. Like most things with coal, it will take some getting used too. The air adjustment on the top door will take time to maximise it's effectiveness, that I remember. Keep a log I might need a refesher course when I get mine up and running.
We few, we happy few,
we band of burners