Is there a way to align two planes in SolidWorks?

I have two blocks that were originally converted from point cloud data and are now solid parts in SolidWorks. I am wanting to use the combine (subtract) feature in SolidWorks Part to remove the common geometry between both blocks. However, without a way to automatically align the two blocks the combine (subtract) feature does not accurately delete the common geometry. I have tried using mate to align the two objects, but because the point cloud data was converted to a mesh and then a solid part, it is challenging to choose a smooth surface. I am thinking of aligning based on the top planes I have created, but have not been able to select both planes to mate to (see attached). Is someone able to assist with how to mate these two blocks in order to use the combine (subtract) feature?

SolidworksAssemblies