Throw the stock ones in **** can and order a set of 1/8 wall tubular ones from Jegs they are about 300 for fixed and 340 for adjustable. The stock one still flex unless you totally box them in as the wall is just too thin.
Also change out one at a time if you are doing it alone.
Beats the hell out of trying to get the old bushings out and the new ones in but you will still need new bushings for the rear end.