These look like cool bikes.
I wish Suzuki would dust off the gn400 motor and make a TU400.
The old gn250 motor looks very close to the TU250 motor.
It also looks like a great platform for my dream bike, a standard with a good seat, dual shock, street and mellow dirt bike that can do 2 up on the street with some comfort, enough suspension and low weight to do well on dirt roads and trails, robust and easy to service, and cool sounding.
I had a number of old Triumph Daytona's and they fit the bill, but were flawed with a lot of vibration (broke things), a 4 speed trans, a weak clutch and transmission.
If you could fit a modern air cooled motor in that frame, it would have been great.
I will add this bike to the list of great bikes you can no longer get parts for, the sr500, the sl350, gn400, etc.