So, despite some concern over strength of new bolts, I decided to go ahead and mount the bracket to the Mariner so I could reclaim the space. As I am going to be using it as I fix it up, I decided to try a few things with this knowing that I will probably not get to the exterior for 2-3 years. I used rustleum marine paint on the exterior, and rustoleum professional on the inside, so time will tell how they both hold up. I used the appropriate primer for each.
I made a new wood mount from marine plywod to replace the old solid teak piece (solid 1.5" teak - very cool) as it had a big crack in it, and figured the plywood would be stronger. I also replaced the other galvanized bolts with stainless grade 5, along with some additional heavy duty washers just for overkill.
The middle bracket is mounted and, of course, sealed with marine sealant.
Sooo, here are pics...pretty cool, and seems darn strong at this point.