I checked the install instructions for the # 607-4 and step 2 requires the 1-1/4 inch long bolts:
Starting with the drivers side, remove the two steering unit bolts behind the bumper attachment box. Bolt a ¼” x 3”x 5 3/8” rear mounting plate to the frame as illustrated using the two supplied 10mm x 1.25 x 110mm bolts, hardware.
And then step 5 uses the longer 1-1/2 inch bolts:
Now, bolt the rear of the brace to the flat mounting plate using two ½” x 1½” bolts, flat washers, lock washers... view full answer...