Green’s Dictionary of Slang

brace of... n.

SE in slang uses

In phrases

brace of broads (n.) [SE brace, a pair + broad shoulders]

[1940s] (US black) one’s shoulders.

brace of hookers (n.) [SE brace + ext. of hook n.1 (1a)]

[1940s] (US black) one’s arms.

brace of horned cows (n.)

[1940s] (US black) a pair of aching feet.