look how hard the 10.5 tire guys run and that's harder than alot of cars running a wider tire but there suspentions are set up to the max.
with a full stock rear stiffer springs arent always better because the make the bushing the binding point and break contact when the bushing unloads
as for boxing the rear lower control arms here's a link for it.
if your try this try and find some from a 4 cyl car they have smaller bushings
http://www.stangcrazy.com/tech/techa...kcntrlarms.htm