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[clamgulch]

Someone else posted a different suggestion for expanding the pipes and I tried it and it worked perfectly: Use progressively larger sockets in a bench vise that are a snug fit inside the pipe, get out a hammer and start whackin' that eroded area until it expands.
Crude but it worked really well and was perfectly round when I was done with the erosion/scarring only half as deep. It'll do for now.

Also, here is a hint- with the tranny out, the up pipe work is a snap, so if your tranny is going to be coming out at some point, plan ahead and take care of the donuts then. You may have to do them now as well, but do them again with the tranny out and buy yourself a few years of ignoring them. After all, ignorance is bliss...