pan needs all that rust out looks like you did not try the molasses .yes grit marks will not hurt but makes it harder to clean. but you can not get in the seams that is why you need rust eater like molasses it is cheap and works or navel jelly .if you can not get that pan clean ..clean ..very clean .throw it away buy a new one .or just pay to have your engine rebuilt with all that junk thats going thru it with that pan if not clean .no way in hell i would not use that pan if you can not fill it with a cleaner like i listed .your never going to get to all the parts you can not see or get at