If you had as much brains as guts, what a clever fellow you would be! a saying to a stupid fat fellow. To have some guts in his brains; to know something.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Braggadocia * Bran-facedNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes