When do you need subframe connectors

I have been driving my 68 Formula S with its 416 for a couple years now. Built and fully ported by Lapouttre racing at that time following a 10 second build he did earlier that year. It has a 3.23 open 8 3/4 so I haven't been too concerned with the torque this thing makes. The right rear just goes up in smoke (even at 55). I am thinking of putting a sure grip, locker or such in it and some 3.91's. A torque strap is a must as I think I am already ready to tear this out but at what point will I be risking things if I don't have sub frame connectors? I am sure I need some trans mods as well. Please let me know what you think.

Thanks