The original guide is here:
https://xpoff.com/threads/19-legion-gear-prep-guide.67478/
I wasn't able to buy the old-school insiginia from the vendor that wowhead lists. Its possible it may be grandfathered now.
Speaking of grandfathered - check your bank for talbar mantle, trailblazer boots, grizzled boots, etc. Lots of the old stuff is probably BiS again.
It sounds like everyone's BiS is going to be:
Head: Rogue WoD Masks (100) or Mist Piercing Goggles (90)
Neck: Problem Solving Pendant (80 - sold by griftah in shatt)
Shoulders: Alliance have a 32, otherwise nothing/BG box
Back: Random dungeon cloak (25) until BG box
Chest: Alliance have a 25/26 until BG box
Wrist: nothing/BG box
Hands: nothing/BG box
Waist: Alliance have 32, otherwise random dungeon (25) until BG box
Legs: Tuxedo Pants/Haliscan Pantaloons (35)
Feet: nothing/BG box
Rings: The Rockx2 (90)
Trinkets: Master Angler (65), Insignia(60, GFd?), AGM (55)
Off-hand: Statholme Lily (70)
Weapon: Emil's Brand for alliance (32) or otherwise nothing
Not sure exactly what can drop from the BG box. Wowhead isn't updated yet.