I'm sure the mags tested the IT400 by itself, but there were no other two stroke big bore Japanese enduro bikes in '79. The 390 Husqvarnas were about the same size motor, but cost way more than the IT and I don't remember ever seeing a comparison.
Found it on the web, but remember the issue as it was one of the first issues of Dirt Bike I bought. The F will have a different frame and better suspension, but I think the motor is pretty similar to the 'C' model.