Fun fact: It was said Pit Viper (the vehicle) was going to be DLC for TMPS3 until Sony decided against giving the game DLC.
I actually knew about that. Did you know that Pit Viper was going to be in Twisted Metal: Lost? I own a little booklet that came with my copy of TM Head-On for PS2. On one of the pages, you can see an image of Pit Viper. I even posted it on the Twisted Metal Wiki a long time ago.