Green’s Dictionary of Slang

(US black) a young man dressed in bell-bottom trousers and a wide-lapelled jacket.

1971		H.E. Roberts Third Ear n.p.: gowster, gouster n. a young person who wears or likes a certain type of dress, e.g. the wide lapels and bellbottom pants style of clothing as opposed to the continental type suit.
1972		Ellis & Newman ‘The greaser is a “bad ass”; the gowster is a “muthah”’ in Kochman Rappin’ and Stylin’ Out 371: The outstanding clue to identifying the greaser and gowster is style of dress. In both cases our respondents stressed their appearance as characteristic of the role in saying, ‘He looks like a raggedy gowster,’ or ‘Greasers dress different. They don’t care about neatness.’ An ideal description for both reveals baggy pants, big-collar shirts, Italian knit sweaters, pointed shoes, and black leather jackets or coats.