They will probably just hack off anything after the suitcase muffler and you can tell them what to go with from there, I just had 2.5 inch done on my SRT8, the stock piping back from the suitcast was 2.75 and I don't know that the 5.7's come with. Before you all talk about how I increased exhaust restriction, the stock setup crimps down to at leat 2.25 in a couple spots so it's moot - and I picked up a little at the track too so it must have helped a little.
I wish I would have thought ahead like you though, because I kind of had to take the only acceptable option they had that would look right and I had to pay $50 per tip!(They are polished stainless though) That brought my total to $250 which I thought was a bit high, but I am pleased with the quality of work I had done at that particular shop and it was highly recommended to me. Good luck, I like the sound...deep bass exhaust and as good as anything until you compare it to the very racy sounds of the CORSA or ZOOMERS.