I've never heard of stock pipes not fitting. How about hanging the pipes loosely on one header bolt, loosening the hangers as much as possible, and then stabbing the pipes?
I tried leting them hang down with barely any nut threads used, and the holes were just beyond popping into place.As it is now the pipes are mounted but the bolts are below the hangers.I will have to use a muffler strap and rig something to keep the weight off.Stock pipes are heavier than the six over six.