It's a lot of meashuring and cutting with an angel grinder then point weld it to the right shape... thats how far I got at the moment. Now its time to cut the tubes away from the dummy flange and weld each joint together. This will be an 4-1 manifold so the collector is the next thing to do, after that there will be a detachable joint to the flextube which is directly welded to the cat which is mounted in the original place of the original cat.
And thats all made of those angle sections you can buy? It must take a while, but I'd imagine its worth it.
What do you do about vibrations from the engine? Didn't the original have a Stainless Steel woven thing to allow for some slop, or isn't it really a big deal?
And as you said, you will need a flextube between the manifold and rest of the exhaust system to take care of the vibrations from the engine.
Pictures of the exhaust system mockup:
It's only point welded at the time because I will have to make adjustment when I create the final brackets to hold it in place. There is a bit of work left...
It would have been better to put the exhaust tube right out thru the rearclam to the right just after the backbox. But I want to have it in it's original place... I was planning on another type of back box in the beginning but that was out of stock so I made the most of what they had. The design is probably not ideal but it will be better than the original since it's 2,5" all the way. I have no idea how loud it is... We'll see in a couple of weeks maybe I have to make some changes then...
Well it's all about trial and error anyway...
Oh, and the end pipe/pipes isn't finished yet, as you can see in the pictures... I'm not shure about the design yet but it will probably end up looking as close to the original as possible (well the pipes will be much bigger).
2.5" bore will be quite loud 
Edited to say I thought Dude had some piccys in his L850 rebuild thread..but only exhaust piccys
I may take some pictures on my own engine tonite, tho
