Let's see...
Artillery/Specter is a Battlewagon with kannon or lobba.
Attack bikes are Warbikes with rokkit launchers (not possible, what about Deffkoptas?)
Avatar mech is a Gargant.
Avenger is a Battlewagon with kannon.
Beam Cannon and Widow are Battlewagons with zapp guns.
Cyborgs are cyborks. Bigger ones are Killa Kans and Deff Dreads.
Flame tank is a Battlewagon with a fuckload of scorchas.
Raider buggy is a Wartrukk with big shootas.
Scorpion tank is a Looted tank or a Battlewagon with zapp gun.
Spider tank is some sort of Deff Dread.
Stealth tank is a Wartrukk, Looted tank or Battlewagon, whichever can take the most rokkit launchas and is the fastest.
Venom is a Deffkopta with blasta.