Fuselage: Forward mid fuselage side structure. Upper longerons.

The plans call for a diagonal notch be cut out of both F-01418A-L/R upper longerons.  As of yet, I'm unable to determine why that notch needs to be there (update 4-Sep-15:  It's to make room for the seat back brace).  I used my Dremel with a reinforced cut-off wheel to inch up on the boundaries of the cut then finished them off with judicious use of a file and 220 grit.

The longerons are lengthy and given their importance in the structure of the aircraft, I wanted to make sure it was properly deburred and super-smooth. I used the Scotch-Brite wheel and 220 grit on a sanding block.

The plans call for the F-01488-L/R upper engine mounts to be match drilled to the longerons.

Update 25-Feb-15:  On first look, the F-01488-L/R upper engine mounts seem identical.  However if you inspect them carefully, you'll notice the forward face has a very slight angle to the vertical.  Stare at it long enough and you'll see it.  So, it's easy to interchange these parts even after matching drilling.  Below is a disambiguation image provided to me by Van's.  Note:  In the image, the part is oriented upside down relative to installation.

I did the right side first with a hand drill.  As you can see, I did a very poor job.  Apparently I didn't hold the drill straight.

I couldn't in good conscience keep the right longeron and upper engine mount in the plane with those holes.  So I had them replaced.  Here's what an AD4 rivet looks like when placed in the one of the worst holes.  That's no bueno.

Turns out a replacement F-01418A-R longeron is $33.70 whilst a replacement F-01488-R upper engine mount bracket is $42.70.  And the crating charge is $15.  It was the perfect time to get replacement hinge for the seat back brackets though.  So on the left and replacement right longeron, I used the drill press to get perfect holes.