Look at the photo. Sure looks like an RB id pad to me, exactly north of the distributor cap
Look at this photo. An RB engine has a horizontal ID pad (parallel to the ground) and this one is visible immediately to the driver side of the dist. hold down clamp, and immediately forward of the bolt you see on the far driver side in the valley pan hold down.
This ID pad has some other info, plant, shift, etc, but at the LEAST it will say 26 or 426, 44 or 440, etc.