Thanks one and all. I couldn't find a voltage spec on the 555 booklet; decided to go for it. And, yes, selected shutter speed (100 sec. equiv) and f/8 manually; the digithell camera is still working fine. The images looked fine, even in that dark restaurant; and, since I was using a strobe on a "L" bracket, no red-eye to try to remove.
Thanks again, for all your input.
The Sunpak 555 is a thryristor unit can be adapted to the electronics of film slrs on those machines that have those capabilities. I would not have considered using an old Strobonar or Metz potato masher on that circuitry. As of this morning (ca 14 hours after the shoot) the Nikdon D50 dighithell camera is still working. Thanks, again, to the advice I have received.
Before digital came along all flashes were designed to work with all cameras and all cameras were designed to work with all flashes.
I think the current low voltage flash sync. ideas are just paranoia and mythology.
The current low voltage flash sync is due to the fact that new cameras use solid state switching device (SCR, transitor etc..) rather than simple dry contact. The solid state devices don't wear out with repeated use but are not easy to make them work with a wide voltage range.
It was certainly possible to fry the electronics in an SLR with electronic sync not designed for use with studio strobes before digital, and even mechanical sync contacts could be degraded over time by arcing from high voltage shutters. I don't worry too much about the mechanical sync with my Norman portable and studio strobes, figuring that it's one of the things that can be adjusted or repaired with a regular CLA, but with electronic cameras I use a Wein Safe-Sync to reduce the trigger voltage to safe levels. The risk is probably low, but it's easy enough to avoid.