Here are the scanner frequencies I was able to verify at the Dallas Grand Prix 16,17,18 September 1994 The superior (and loud) PA system and very good announcing almost negated the need for a scanner!
SCCA Corner Workers: 464.425 (I rarely hear them any more at their old 151.625)
Race Control: 469.925
PRIME Director: 455.675 All the live interviews sometimes race announcing (but not always???) sometimes directors calling the shots
WORLD CHALLENGE 488.5625 Mauro Baldi #70 Porsche 911
TRANSAM 468.9750 Ron Fellows #4 469.8500 Dorsey Schroeder #12 466.8875 Jon Gooding #16 468.3500 Brian Semo #22 (Previously Boris Said) 460.1875 Paul Gentilozzi #28 465.8250 Bruce Barkelew #71 463.5125 Ray Kong #87 467.3875 Tim McAdam #94
I never could find Scott Pruett, Jack Baldwin, or Tom Kendall at all, nor did I find any hints of them being there, but scrambled