"If we were to scan them in, can I use Vegas to turn it into a modern 3D Blu-Ray disc?"

In the absense of any reply from someone better versed in 3D and Vegas and from my own experience I'd say yes. I've taken dual 3D video from a camera, dropped it onto the Vegas T/L, synced it up, told Vegas it was a 3D pair and put on those horrid anaglyph glasses and got 3D. I see no reason why you could't caryr on from there to create a 3D BD disk.

Probably the trickiest part will be splitting the scanned prints into left and right eye images and keeping the correct separation and alignment but once that's mastered it all should be just mechanical.

Bob.