I think the DC's are 1-3/4 IIRC. So you want to go with a 1-3/4 stepped to 1-7/8, straight out of the head like the one pictured, standard 2.5" collecter with reverse cone and megaphone? Sounds good in theory imo. The only thing you will lose if you go straight 1-7/8 will be a little low end, if your not worried about that then dont waste your time. If your only reving to 7K you may not fully benefit from the 1-7/8 though