Front spring u-bolt size

I've got a 40 Chevy truck cab, frame and bed. I am using the original front axle and slid it forward. I fabbed some bat wings I hope will work. Fabbed a front spring bracket for middle of spring to frame. I was wondering what size square u- bolts everyone was using. Any help would be appreciated. I need to get these soon so I can attach front axle. Also ordered the speedway super glide 26" t-bucket spring perches and shackles. Will this spring be stout enough for this truck with 350 and no front clip?

Ohh I forgot... It's a 1 3/4 wide spring but need to know diameter of bolts.