If you have any idea who it was that made the instrument, or had it made, check with them, at least for reference, and see what tuning and playing styles they had in mind when the instrument was made.

Check this link, Tunings and browse around the site a bit, because it gives not only tunings(it seems like every steel player has his own tuning)) but some good background on what the advantages of different tunings are, as well as some insight into what the whole process of steel playing is about.

There are a lot of very informative steel-related websites--also, in case you don't realize it, lap steel and console steel are pretty much the same animal, and the playing and tunings will be the same. A pedal steel is a bit different, since tunings are often the way they are because of the chord changes it allows with a pedal or level change--

I am not a steel player, but have worked with a number of them and have always been impressed with how involved instrument the instrument is--you have to like figuring stuff out, and you have to know exactly what you are doing all the time, because otherwise, you're lost--