What KTM said there ought to tell you that having to do some grinding on the edges of the sections to get good fit-ups for welding should not lead you to worry too much about losing some dimension you get from a software program or whatever. Those programs give the illusion that their dims are right-on-the-money, having been calculated mathematically. This illusion of accuracy is rather like what you get with a set of 6" electronic calipers that read clear down to tenths of thousands when the jaws of the calipers are not capable of such accuracy (nor are most users). Make good-fitting joints and weld them up and try the result. Maybe one pipe will come in a few hundred rpm before the other. Is that necessarily bad? It might actually make the bike more pleasant to ride.constructing the pipe initially is childs play for some one experienced. what sends the price through the roof is taking it apart 20 times and changing the dimensions trying to find the most power.