If you are going to get the 355 mounted into a copal #3, Grimes gets $475 for the shutter plus mounting. I do not think it is a direct fit, and if not, you are talking probably in the $500 range for labor. see the S.K. Grimes web site, or call them.
Some fit directly into a #3 shutter, and others don't. I had one that didn't. You'd have to ask schneider or SK Grimes if the one in question does fit directly. In my opinion they're are better options than spending the $500 on having it mounted. (For example, I bought a 420 Fujinon L mint in shutter for $200 from a reputable dealer. For 8x10 work, I'm very pleased with the lens.)
My hesitation on the 355 without shutter would be more with the seller, only a single feedback. Could be high risk. I don't work with low feedback sellers unless they're near enough for me to close the deal personally.