2wd shafts are differant
if your still running the 4x4 then its not just as hard on them obviously
its usualy box's and front diffs that go
but the rears do blow up as well with big power

welding them wont realy help it'll just put you sideways into every corner

if your running a genuine 450bhp on a 4x4, then you'll be needing a box and front diff 1st(soon)