i had the recall done too and took my car in and they had it for a whole day then 3 days after that the engine blew up, they replaced it but it took like 3 weeks and was a huge pain in the *** hopefully that doesnt happen to u lol
you know what same thing happen to me with the SES and the whole oil thing... basically i got a whole new block... and it was all good. Took only about a week and a half to take care of everything. car is better than ever now..
420 is precat efficiency... its probably blown completely empty. hollow
get a header and a quiet cat-back when you get the motor and you won't have to worry about it. If you don't have motor mount inserts, you should be fine in terms of noise.. if not, just deaden your tunk some.
header install is easy, even if you have a visual inspection, you can swap the manifold every year or three for the emmisions.. it's not that big of a deal