do the magnaflows change the stock location? catco and eastern make a direct repalcement but they are still only 49 state legal, they look like stock though IIRC. if you have someone in another state that you can have them shipped to and then have them shipped to you, you should be alright. or you could buy some used stockers from the for sale section.
For what its worth..........
I swapped out my 05 GTOs mid-pipes with high flow catted mid-pipes.
I have the factory Mids still with about 10K on em.
iirc, 05 GTO cats are 2 1/4 inlet and 2 1/2 outlet.
Laws in CA are tough.
leme know if i can help out.