Yup same with mine!! Don't worry just use your jack handle for an additional 4 ft of leverage. Worked good on mine. 
4'.....be real careful. If those are 9/16 U-bolts it won't take much to break those or damage the threads. At the very least you could over stretch the U-bolt and it could break.
DO torque them with a torque wrench. They won't get tight enough with an impact no matter how long you "ratatat'' them. I used 5/8 U-bolts on mine and they only torque to 110-120...plenty tight! Mine are stock chevy rears with the chevy spring plates that fit perfectly over my V6 rear end housing. Couldn't ask for a better fit.
