Anyone swapped out Magnapacks for Magnaflows?

I called Magnaflow and they tech guy said either might fit, he was not sure. He said the tailpipe part of the catback might be a little different. Do I need offset/offset or offset/center? I ordered a set of center/center thinking they would match right up with the packs position and boy was I wrong, oh well!

And whats the difference between the stainless steel and aluminized mufflers besides price?

14336 off/off
14326 off/cen