How much towing capacity does a vehicle need to tow a 67 GS400?

For years I thought equalizer hitches were for sissies. When the place where I bought my enclosed trailer strongly recommended one I finally gave in. I would now not tow any 4,500 lb and up trailer without one.

 

I tow a 7500# boat and trailer with an Escalade ESV. Truck rated at 8K, receiver hitch rated 12k and ball and receiver insert at 15k. Trailer has brakes. I don't even know it's there. All parts have to exceed weight rating of total weight of what's towed.