"I never thought we’d get a guy of his stature to wear a period piece wool costume in 90 degree weather for 10 days straight," McBride says of casting his surprise Civil War-set final season opener. "And for no money.

After two TV series focused on pompous protagonists ("Eastbound & Down," "Vice Principals") behold the finale of his third, "The Righteous Gemstones."

I sent him the script and he called me back pretty quickly,” McBride tells PEOPLE before explaining what happened next