Rear suspension install questions on a 66

[msg]

When I did the tear down years back the coils had only this hardware in the pic holding it in. The manual is a bit different even though its a 63 manual I figured its close. But the 63 must have had a welded square bolt there. In my case there is no welded square nut just a hole. So I think its just one nut holding the coil on...seemed like it might need a washer but I guess it doesnt. This seem right to go with? Or is adding a beefy washer going to help? In the pic I havent tightened up the top bolt yet.