Called Southern Nikonos before buying anything, and talking with Bob gave the last bit of encouragement I needed. Everything is going to him before it goes out to sea with me.
Also, ordered Church's book simultaneously with the Nikonos V! :-)
I did a PADI U/W Photography course at Stuart Cove's some 9 years ago, using the Nikonos. I got some terrific results, just with the 35mm lens. For now, I'll miss not using digital, but on the other hand, the space saving of not carrying a dome is significant.
The tradeoffs are large, but not all of them are bad. Truth is, I'd have given my eye-teeth a decade ago for a Nikonos rig (much of it new), secured for a small faction of original cost, and a good deal less than renting a Sea&Sea.
Got this one last year though, with the Sea&Sea/Nikon D200: http://billkeane.zenfolio.com/p687018592/h3b07a628
Thanks for all the help and insight here!