Green’s Dictionary of Slang

ace-deuce n.2

also acey-deucey, acey-doosy
[lit. ‘one-two’]

(US/W.I.) a best friend.

[US]C. Cooper Jr Farm (1968) 170: All the acey-doosies and heavytalkers.
[US]Bentley & Corbett Prison Sl. 38: Ace-Deuce also Acey-Deucey Old prison expressions used to signify best friends.
[US](con. 1975–6) E. Little Steel Toes 109: So do your ace deuce, cross-eyed road dog a favor, keep a low profile with your city ways.