After I posted that last night, I realized I screwed the pooch AGAIN!  I cut the length to fit the inside dimension of the box and didn't allow for 1/4" lip on each end to be dadoed into the case members 😡  That's what I get for measuring instead of looking at the plans...  Fortunately it won't affect the build significantly.  Just dadoing it into the top members will make it plenty strong enough so no real harm done.  Good thing too 'cause I ain't buying another piece.