[GVS]

I don't have a definitive answer to your question, but it is my understanding that Ron Butler Racing supplied 60 chassis to Arntz at the end of the Type III run. These had a "BR" and the chassis number stamped into the front of the chassis.

When Arntz went out of business in late 1979, Ron Butler bought Arntz's molds & inventory. Ron Butler Racing built an additional 104 vehicles between 1980-1994. Ron Butler Racing cars have a stamped number on the front of the frame on the drivers' side, just behind the bumper mount which starts with BRI. The digits after BRI represent the month, year, chassis number. For examples, SoTxButler's chassis number BRI391086 which decodes as March, 1991, chassis#86.