How to cut angled pipe for a segmented/lobster back bend?
I think the answer in both cases is a handsaw in a mitrebox. For 200mm pipe, that's probably going to be a home-made mitrebox with 250mm tall sides and 200-202 mm between the sides. 



The simplest solution to the second problem for relatively short segments is to make the box long enough to cut both angles without moving the pipe, and clamp it in place - perhaps with wedges, or perhaps a strap clamp or hose clamp attached to the bottom of the box.