as above, weak coils prob fouled old plugs, just change them, haven't heard of those coils, maybe they're getting weak already, go for .8 plugs
(this isn't forced induction performance related haha)
This!, I recently sold a VE SV6 & i've many DE daily drivers, unless the sv6 has something big time wrong with it, it will dish you a beating, an exhaust that big on an NA will just be a megaphone
this, the shim will only tighten the lsd action in the cheapest way, apart from welding it haha, the metallic ting sort of noise when put in reverse will be backlash which is just from wear, I'd prob just put up with it until diff upgrade time