It's not just a matter of personnel and the equipment. There's a whole infrastructure, including logistics, legal, security, etc, supporting these weapons that would need to be replicated or expanded for surface vessels.
Mods on existing ships has been done before...logistics/legal/security for boats with nuclear weapons are already well established and these converted ships would probably have to be either relocated to where the SSBNs reside or new facilities would be built that mirror the SSBN bases...in any case, I don't see it as being "impossible" to accomplish.