OK- Larry won the Class 6 title in 1983, and the rules for 1984 were changed to limit engine displacement, but that didn't hold and Class 6 was again open to all production sedans except for VWs again that year. And as for Larry's Chevies, he raced 2, the first used 3.4 ton Suburban front clip and was later called illegal for the class and the second Tri5 Chevy was built and the first car became a wagon chase/prerunner. here are the rules from back then-
Vehicle built from 2wd sedan or wagon, series produced with at least 2,000 units in 12 month period, No VW or Porsches allowed, Corvairs OK. Coupes,convertibles, station wagons and passenger pick-ups, such as El Caminos and Rancheros included in this class. Sedans, The following 4wds allowed- Subaru Brat and station wagon, AMC Eagle and Spirit and Audi Quattro. Others may be considered.
This is a stock production class and parts will remain stock except for those parts allowed to be modified. Rally Cars meeting F.I.A. requirements will fall into this class.
Suspension- Other than parts mentioned, all parts will remain stock but may be strengthened with additional materials. Suspension pieces may be interchanged within the passenger vehicle series of the vehicle manufacturer. Suspension must maintain original manufacturers concept for the vehicle series. All springs must maintain original concept. Items with no restrictions-Spindles, Pivot Points, Spring rates and capacities, Ball Joints, Mountings.
Number of shocks and mounting methods optional, however, shocks may not be mounted in passenger compartment without approved metal shield cover. Spare tire must be located in body.
Steering system must maintain stock type (rack and pinion, reciprocating ball, etc...) but may be replaced with same type but must remain in stock location. Idler arms, tie rod ends, tie rods, ball joints, pitman arms, etc... may be strengthened or replaced.
Engine displacement was initially limited to 2850cc's (173.9 cu. inches)only real restriction was no dry sumps, but the class kept getting big engines cars and Class 6 and Class 6B went back to Class 6 shortly after.
Transmission was to be same as body manufacturer. Rear ends were also to match body manufacturer.
Firewalls were to remain in stock location, intact, and whole.Completed must weigh Kelley Blue Book listed weight minimum. Floorboards could be modified for exhaust routing. Fenders could be cut up to 4" and flared maximum of 2" except for Citroens that could have the entire fender opening in the rear opened up to expose entire tire. Fenders must be attached with bolts, No one piece hinged front ends. No fiberglass fenders.
Stock Wheelbase must be retained. Frame may be strengthened. Body must be mounted in stock location. Tailgates and trunklids optional, hoods and trunks may be of any material. Safety Glass windshields required, side glass optional. Stock Grill mandatory.
That's 1984.