Hi Tommy!
How are you going to mount your engine? I just finished my 28% Katana with DA50 mounted cylinder down. When mounted that way the perfect header is doublebend header with 25mm drop. Oh, and I don't know if the 'normal' drop direction is towards the plug or what because when I first ordered a 25mm drop header from KS they managed to send me a header that had drop towards the carb of the engine... Ofcourse it didn't fit at all... But the second try I got the 25mm drop to the other direction and it fits just right.
I am using a KS1060 tuned silencere on my Katana and so far after 4 flights I am very impressed with the performance. Katana is surprisingly sleek flyer thanks to its thin wing profile, but yet it can be flown soo slow because of the huge wing area.
Mine ended up at 18.6 lbs (8450g)
You really can't see the header from my pictures that well, but I hope that the idea can be seen.