It's like this.
If you want to be a baller and build wyyyked shit, get a chop saw and a welder and make it work. Not very hard to do, and you'll be able to mod anything steel after this. It's super important to being a competent moped builder.
And don't go trying to bend a bk100. It'll crack super fast. Better to chop and weld.
And lastly to pipe length and the comments that it has to stay exactly the same length, well....that's bullshit. Change it any way you like, shorter header, longer, etc. it doesn't matter.
You might get a lil higher revs, or slightly less.
Modifying a header takes a LOT of removal to change the power.
1 inch of header removal only equals 400rpm. The only thing that will fuck up your shit is if you mess up the welding and leave mismatched pipes blocking flow, or leave slag inside the pipe that will kill your engine when it gets sucked back in to the cyl. ALWAYS CLEAN OUT A PIPE WITH WATER AFTER WELDING TO FLUSH OUT ANY LOOSE DEBRIS