Kim, according to the CRG chart the IL code is 67-69 BB auto...but the 67-68 big tank had OM....when you think about how few 68 BB Nova auto cars there were (L34/L78) it would make sense that they would have used the Camaro ones they had on hand
the Gibb cars were a late production run and perhaps the radiators were already in the works for the 69 model year..that would explain the 69 code....maybe drop an e-mail to Wayne...he might have some info from John's car.
wilma