Since they'd be so long, if you run them out of 1/4" plate, I'd probably add a little gusset in the middle. Highly unlikely something bad would happen, but the longer they are, the more susceptible to getting bent out of shape they are..
edit: like you said, farm beater, but really long shackles will actually increase sway etc.
"Chilton's and Haynes are for brake jobs, oil changes and starting campfires." - CJ7-Tim
'98 2dr/5spd Cherokee rockin' on tons, 5.9L V8 Magnum, HP60/14b, 5.13:1, locked, 14" coilovers, Dana 300 4:1 twin stick... oink oink!