I don't know offhand, and the cells that you have may not be the same as those that someone else has, given how widely those cells have been distributed over the years. However, it is easy to determine DNA content per cell simply by staining with DAPI or some other DNA dye and analyzing by flow cytometry in comparison with primary mouse cells, which should be 2N.
I would agree with the above, staining DNA with prodium iodide and running FACS analysis would give you an idea of ploidy, then compare with other cell lines. I'd try a few passages of MIN6 if you can, as MIN6 cells definitely change during passaging. From experience, >p30 cells have increased basal insulin secretion and I believe this is due to altered hexokinase activity/expression.