Hello again BPI1, if you believe that grinding might be overly burdensome in the preparation of these parts I believe I would consider welding a few test pieces in the "as received condition" and then doing some testing of the resulting welds. Possibly sectioning the piece so that you can view the fillet and it's interface with the round bar and the through plate, will tell you whether there are any issues with cleaning and preparation. Possibly a polish and etch of this section would further reveal issues. Even the visual inspection of the weld itself will give you some pretty good clues as to whether the interface of the weld metal to the base metal has any issues.
The "skin" that I was referring to is typically not of quite the same composition as the rest of the casting due to it being the contact and release point from the mold. Depending on the particular casting process and the care exhibited by the manufacturer, this may or may not have a great impact on welding to this surface. Not having specific knowledge of this, or the condition of the parts that you are working with, is the reason for my mention of it. Also, the intended purpose of these parts can impact the level of acceptable weld performance that is expected and would determine to what degree you would need to go with part preparation. Best regards, aevald