It is a 'D/Dart'
'Chicagoland Dodge Boys'
AHRA in 1966
The 1966 Dodge Coronet {Formula 1, B/Stock} was
a 4-Speed with a 383 with a Dual Carb set-up and a Solid Camshaft.
The 1966 Dodge Dart GT {Formula 2, G/Stock} was an 'original' D/Dart that was converted to a Hydraulic Camshaft and with a Dual Carb set up.
Engine bored +.040" equals 280 Cubic Inches.
The '18' is the Handicap Designation for engines with a 280 to 292
Cubic Inches.
http://img.photobucket.com/albums/v222/gothemi/JackThomas66.jpg