Ok, then it very well could be considered a 36 spline shaft, or something similar, since the number of splines is counted as a whole circle in cases like this.
Sounds like we're going to need a good close-up shot of the end of the shaft then. Both at a side angle showing the flat spot, and more importantly an end shot at just a slight angle.
This way it might be easier to tell if it's the offset, standard, metric or whatever other possibility might be out there.
The only reason to know all this is to match up the correct lower u-joint in a shaft.
If you also inherited some kind of u-joint with the box though, you might be able to reuse it.
Still, better to know what you've got for future reference anyway.
Paul