Green’s Dictionary of Slang

(orig. US) wealthy, rich.

1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 11: Stuffy: Wealthy.
1936		H. Corey Farewell, Mr Gangster! 280: Slang used by English criminals [...] Stuffy – wealthy.
1977		D. Powis Signs of Crime 203: Stuffy Wealthy.