67 specific manual steering box mounting bolts

There's no recess on the aluminum casting. Only difference I'm aware of in castings is the slant six abody cars got a bushing instead of a bearing.
The bolts you show look familiar. I think they may be the same as came on my '67 Barracuda.

I wouldn't worry about it too much. Once torqued down, the split washer will be essentially a flat washer. The torque on the threads will be what keeps them from backing out. Good ol Carrol Smith covers this well.