The 400 was the begining of the fazers and was built for the Japanese home market in 1997 and 1998. The model code was 4yr and many of the 600 parts begin with 4yr. It put out 53hp at the crank
The 600 was derived from it and was in production from 1998 to 2003 with an update in 2000 and a further update in 2002. It has 95hp at the crank.
The 1000 was an addition to the theme and was in production from 2001 to 2005 with the detuned R1 engine with 143hp at the crank
I happen to have one of each in my garage. The big difference in looks with the 400 is that it has Brembo front brakes, a seat strap, no grab rail and no centre stand.
The 400 is a lovely little bike to drive with a power band at 9000 revs compared to the 600 at 7000rpm, never noticed one on the 1000 it just pulls like a train. Oddly enough even though the 400 looks identical to the eary 600 it feels much lighter.