Green’s Dictionary of Slang

as intensifer: to a very great extent, in a very intense manner etc.

1978		S. King Stand (1990) 1171: You’re just scared gutless of him.
1984		Flame : a Life on the Game 58: I [...] visualise myself on my hands and knees surrounded by old cans and bits of wood, getting screwed gutless.
2003		McGill Reed Dict. of N.Z. Sl. 182: send up gutless Make fun of.