Hi, I'm new to WR450s and just wanted to know if someone could give me a little background on them. 1) Could you give me the years of production for each? (400, 426,450) 2) What are the main differences between WR motors and YZ motors? 3) Did YZ (4 stroke) motors come before WR motors, or did they both hit the market the same years? Thanks guys, I'll be here a lot!