Green’s Dictionary of Slang

(Aus.) a naïve, unsophisticated person, a peasant.

1950		J. Morrison Port of Call 66: That ain’t no reason for let to go pokin’ mullick at the bush-’eads. These city sheilas are all the same.
1966		Meanjin Quarterly (Melbourne) 281: ‘See them lyrebirds.’ Jack agreed. The two bush-heads were manifestly revelling in their role as hosts.
1973		J. Morrison Aus. by Choice 123: They’ve all gone, the old employment agencies for bush-heads, the shabby but busy little shops where jobs were bought and sold ... teamsters, harvesters, fruit-pickers, fencers, shearers, boundary-riders [AND].