Any API SM 10W-40 rated oil will have the necessary zinc/phosphate content for the older flat tappet camshafts and is a good choice of oil weight for both new and lightly worn engines. Just be wary of any oil with 30W or less on its labeling as these do have a reduced zinc phosphorus content. Here’s a recent thread that contains links to other discussions regarding oil choices for the Y.
http://www.y-blocksforever.com/forums/Topic56685-3-1.aspx