If that little bit of bolt is lower than the bottom of your rear diff, just get a Dremel tool with a mini-blade and cut them off. Most of the add-a-leaf or rear blocks I've seen have the U bolts set up like that. I've see bolts with more exposed than that and generally the rear diff will drag before the U bolts -


'97 T100 SR5 XCab 4WD
TRD SC ~ ARB ~ FWC
'85 FJ60 Landcruiser
4E9 ~ locked ~ 33's