Matt, Willy,
The rules for the Classes are as follows...
ALL Chassis must be 1994 or older...
Batteries: 2S Lipo or up to 7cell Nihm or Nicad

Classic: is brushed 27T or 17.5 as most are pre-blinky there is no BLINKY Limit, and the remainder of the vehicle must be stock as intended by the OEM ie; no long or extended arms, and orig type tires, no modern tires.

2wd Buggy: 17.5 motor limit and any tire combo you can manage minus 1/8 scale.

4wd Buggy: up to 10.5 motor

Monster Truck/Heavy Metal: Orig motors or up to 10.5 limit and stock batteries or 2S.

Truck: 17.5 limit and 2S batt with no limit on tires (again not 1/8 sclae).

I hope this helps.