Isn't "A" just an open oil return hole?
Seems to me they deleted the oil line in '58. At least the '58 cars that I have seem in the salvage yards were without it...
If you have a shop repair manual for '58, it will show you what to do.
There should be a tapped hole to the rear of the last lifter (but I don't see it in the picture), this hole would be pluged as well as your "B" hole with an 1/8" pipe plug.
