Howard,
Having just discovered the presence of bolt and studs, take a close look to be sure that they are all of the same thread type. The idiosyncracy of my own sump plate is having three metric helicoils and one remaining original thread. This is my own idiot fault, but I know to keep track of it when disassembling. Next engine rebuild, say, in fifty years, I intend to correct this.
Richard L.