NACA 2412 versus Clark Y is in practice not that different. As long as it really is the Clark Y and not some flat bottom profile with the upper curve from the side of some shoe. Note that the Great Plane PT-40 trainer airfoil is something different than Clark Y profile.

NACA 2412 is 12% thick with 2% camber and the highest point on the camber line 40% from the leading edge. Clark Y is 11.7% thick with 3.5% camber and the highest point on the camber line more forward at 30% from the leading edge.