Getting a similar Shop Manual

I wouldn't exactly say Mopar dropped the ball, The Barracuda was a late entry car for 67, production started October 31, 1966. So it is hard to say if the literature was even ready for the press when the manual went to press.

The Supplement was issued as a Service Bulletin, it includes everything unique to the Barracuda, otherwise use the Valiant in the regular Manual
https://www.mymopar.com/downloads/servicemanuals/1967_Plymouth_Service_Manual_Supplement.zip


Alan