yes the backing plate will come off completely. if it were me i'd keep soaking it with the blaster & just wait a while & the bolts will probably come loose. i always like to clean all the loose rust & dirt off the surface with wire brush first. come to think of it, seems as if those bolts go through a hole in the backing plate & are threaded into the wheel cylyinder which you're replacing anyway. there again if it was me, i'd just break them off & buy some new grade 5 or 8 bolt ( cheap ) rather than tear into it that much further. let me know how it works out.
robert
