I sent him your comment and he emailed this back:

I may not understand the one about whether a fleet ballistic missile (FBM) submarine can be retrofitted for a nuclear payload. But there are two nuclear aspects to a U.S. fleet ballistic missile submarine - the nuclear power plant used to provide the energy needed to propel and provide electricity for the ship - and the ballistic missiles that can accurately deliver nuclear bombs onto targets thousands of miles away. Some of the FBM submarines that were in service when I was on active duty were later converted to non-FBM service, and no doubt could have been converted back. I cannot speak authoritatively on that, but think that would have been highly impractical as well as inconsistent with our country's arms reduction commitments.

There is a very impressive Wikipedia article on liquid fluoride thorium reactor technology. (You may want to recommend it to the questioner.) The potential advantages are enormous, but so are the challenges. The only "insight" that I can offer is:

Light water reactor power plants turn nuclear-generated heat into usable electrical and mechanical power using the steam cycle, an about 200-year old technology that advanced to replacing steam engines with steam turbines about a hundred years ago. The as-described liquid fluoride thorium reactor technology doesn't utilize so well-proven, well-developed a technology. (I tend to think of the liquid fluoride thorium reactor technology as somewhat akin to the automotive technology that preceded Henry Ford's first cars.) That doesn't at all mean that modern engineering cannot make liquid fluoride thorium reactors practical and economic, but advocates of implementing new technologies typically underestimate the technical barriers that must be surmounted, the cost of doing that can be incredible, and surmounting technology barriers can involve very time-consuming development of new technologies. A huge number of promising ventures fail because of unforeseen and insurmountable (at the time) obstacles, and whether or not any individual one will prove to be suitable is highly speculative. Moreover, "nuclear" is a button-pushing word that escalates opposition to everything it's associated with.