Black Widow from the UK is the only exhaust company that I've come across that makes a FULL exhaust system for the Hyosung GT250R. Suitable for all carby models, and the early EFI models with just the single o2 sensor in the exhaust pipe coming from the rear cylinder. https://www.blackwidowexhausts.co.uk/gt250r-gt250-comet-441-c.asp#
This was my '08 GT250R the day before it was written off while parked. In this video, I have BW headers/down pipes (whatever you want to call them) connected to a scorpion muffler
Alternatively, you could just get a Radiant Cycles shorty GP exhaust tip to get similar noise levels on idle for about $65 - $70
I got a Arrow race header exhaust pipe, never used and repair manual, cheap. email is interested. adye1@windstream.net