I have an old Vivitar 365 that I haven't used in years. The thing drank "C" batteries like there was no tommorrow. According to : http://www.botzilla.com/photo/strobeVolts.html the sync voltage is 46V. Much higher than I would trust to use with a DSLR. The Wein Safe-Sync is a good idea. Better Safe than sorry.
Another thing to consider is that flash control has come a long way since the Auto flash mode of a Vivitar 365. Nikon i-TTL flash control and CLS is like Magic compared to the old days. Good Luck and Enjoy your Nikons!