Frame Conectors instructions

Bolt on is just adding weight......they will be tight for a short while and then provide less stiffness than you hoped for.
Weld them in , or have it done.
It shouldn't be that expensive or difficult if you have to farm the job out.
I used 2X3 .125 wall tubing and tied the rear foot wells ( floor ) into the connectors where they came through the floor......they T at the torsion bar crossmember and slip into the rear sub frame rails.........just doing that made the car so tight that when I put my floor jack on the spring perch in front of the rear tires , the whole side of the car comes up.
The reason for installing them gets lost with a bolt in application.

Edited to add........you can use the kit , but just have it welded in in addition to or instead of the bolts. You won't regret it.