KEH has both the 350 and 500 in stock. Consider the size of filters you might need . . .
I'd imagine that yes, the 350 and 500 have tripod mounts. The Hasselblad bodies are so light and relatively fragile that I can't imagine another configuration. There's a lot of metal in the big lenses.
Have you thought that 35mm might be a better option for your needs? Faster lenses, less bulk and bother, 36 exposures to a roll, etc.
Yes, I know bigger is better, but shooting from the deck of a moving ship with a huge f/5.6 or f/8 lens begins to make me wonder. You could pick up a bunch of used Nikon or Canon gear and some nice lenses for the equivalent expenditure, including backups!