Glad you realized it was at the Sub Base in SAN DIEGO... you go to San Fran and you'll end up with no gun (but flowers in your hair...)
What does it cost to ship a 7 ton gun? Well if you're lucky, nothing. COD's was delivered one day with 24 hrs notice. Our director kept trying to get a bill for several years and then tried to say thank you to the trucking company for donating the haul from Keyport, WA to Cleveland, OH... finally he was told to "clam up" on the haul -- as in "what haul?" "We don't know about any stinking hauling of a 7-ton gun!!" We finally got the idea.
We had an angel with ties to a trucking firm. We have actually had to pay for hauling 40 mm guns... but like the 5 in. gun, there really is no crating involved. The Gun sat on its wide mounting circle with some tie downs, but no structural crating that I recall. I will check with others involved in receiving the gun to confirm this. When you ship items like guns, the trucking company needs to know how to classify the load... apparently there is a big old catalog of categories... and some categories carry special provisions... like the gal on the phone who was all set to give me a price for the 40mm guns I needed to have shipped to COD and was about the quote it on "Guns... operational, military, DoD, ATF-registered" which was about four times the cost of shipping "Guns, ORNAMENTAL." Later I was told by someone that shipping the damn things as "Scrap metal" would have been even cheaper and involved less paperwork."
If an angel doesn't flutter down on alabaster wings, let me suggest you put the word out among all friends and visitors that you need someone in the interstate trucking/hauling business. Remember, time is on your side.. they can haul it when cheap and convenient since your sub has gone without the gun for so many decades, a few weeks or days will not matter.
Another point I want to make... your 3-in. gun is probably a surface 3-in 50 cal... not the submarine mount. The USN had Nash-Kelvinator Co. make the damn things in the thousands for use on everything from minesweepers to DEs... They were good dual-purpose guns... that is they were rapid firing for surface targets and had the ability to engage aircraft... but another technical innovation, the proximity fused 5-in. round made them all obsolete. So the USN shipped them ashore as fast as they could. Rather than try and swap, let the vets know what you need. The decision on what to replace any wet mount gun with at Ballast Point Submarine Base's submarine memorial is up to the NAVY... and they would likely be inclinded to add a more modern reference to the memorial plaza, say a missile body. Again,this is not some Arab camel trading bazaar... but rather a natural and intelligent process by which a lawn ornament finds its way back home where it belongs! The vets don't own the plaza so design matters will be more in the lap of some NAVY officer than the local vets. But their permission is needed to get the wheels turning. Good luck. It's nice to realize some progress on a process I started over a decade ago.
Paul Farace