To be quite honest with you on where to mount the lower strut tabs------I looked at the picture on the box
and then took the center-center measurement between the tabs on the top wing and applied that to the bottom wing. Had the struts connected to the top wing, fit it into place and making sure there wasn't any "rack" in the top wing by measuring between the corners at the trailing edge to the stabilizer, letting the struts hang into position at the measured points, look at the box again, place the metal angles on the wing, look at the box again, take the "hand drill" and go for it......apparently I hit wood 'cause its all tight as it worked out---no need to cut and add a ply plate. No problems to date, it all stays tight, although the top wing will rotate forward/aft just a bit when you work the ailerons due to the twisting of the single cabane strut.
I imagine the "starter holes" for the angles are in fact pre-drilled in the bottom wing, just that I couldn't find them under the superb covering job just by looking. You might try and hold the wing over a very bright light and see if you can discern the holes......or perhaps heat the area with a monokote iron and see if the holes appear?
For what it's worth, on mine anyways, the holes for the tabs in the bottom wing wound up in the white area between the blue and grey covering; the inner hole is just a fuzz forward of the grey and the outer hole just a fuzz rearward of the blue.
BTW---unrelated to the wing mounting, I did add a 1/4 ounce piece of lead to the top of the engine mount right behind the firewall on mine----had it balanced to plan before and it flew just a tad tail low---the little piece of lead made a world of difference in the handling of the plane.