I would never weld the pipes to the headers...If you ever have work on heads or anything else where the exhaust is blocking access, you will hate yourselfs for doing so... 
If you straighten the flanges and weld the flange to the header ( just some strong tagwelds between the boltholes ) you will gain a lot of strength , and you won`t have to take the flanges off the headers, which save a lot of work and time. If you decice to go this way you have to make sure you have access to all 3 bolts for wrenching... 
Yeah, I've decided to not have them welded after all, even if it's the quickest, simplest, and cheapest
short-term solution.
I just know some $hit will happen then, that requires the headers to be removed.
It never pays to ignore the Law of Things Inherent Evil.
So tomorrow morning, I'll probably go to the muffler shop again, and wait for a turn. See if I can have the old flanges straightened out.
If not, I must try to persuade some metal workshop to make me four flanges the same day. Not very many of those in or near Oslo, according to google.
I have an extra set of TTI header reducers if you want them.. 2.5"
Thank you very much man, but I got a 3" collector.
Besides, TTI stuff on those pipes would be pearls before swine. 
