My 1950's home has all the cold air returns in the inner top wall coming out to the inner hallwall. I am replacing a couple of the grills and am not sure if the grates should be angled down or up. I am thinking down so I can capture more cold air, but am unsure.

The return grills do not matter which way they are facing. Ideally you want them to face so you cannot see into them.

Supply grills however do matter a bit. Ideally they should be the adjustable types that allow for you to face them up in summer and down in winter.