However you decide to go, use both the connectors and the boxes. Consider tying the front frame rails too. US Cartool does have a nice chassis stiffening kit, but it is more than doing it yourself. I have their kit in my A-body and it transformed the car. The car did come with front and rear torque boxes along with the other factory mods that come with a convertible.
I found my front shock towers were almost completely broken loose at the spot welds to the inner fenderwell. I welded them solidly to the inner fenderwells and also welded up my K-member.
