I'm not an admin so I can't give you the data you're looking for, but Flite Test already has in the form of the plans.
You can get the dihedral angle from the plans using the dihedral gauge on page SHEET-3 and the 1/2 wingspan from page SHEET-1. The wing assembly video shows you which points to measure from. The 1/2 wingspan will be the hypotenuse, the dihedral gauge height the side opposite the angle you're looking for. Sine is opposite over hypotenuse, so just divide the gauge height by the 1/2 wingspan and take the arcsin of the result. As long as you use the same units for the opposite and the hypotenuse it doesn't matter whether you use imperial or metric or pixels off your screen. As long as you use the same scale when taking the measurements it doesn't matter which page of the plans you use. Just be sure to have your calculator set to degrees, not radians.
The box has to fit snugly into the A-fold in the main spars, so you can get the box cross-section dimensions from SHEET-1 in the plans. There are inch and cm scales up in the top right corner of the page. You can use those and a drafting scale to get the actual dimension of the inside of the main spar A-fold.
Once you have those dimensions from the plans, you should be able to compare them to what Fusion 360 tells you and make any necessary scaling adjustments to the length.
Finally, keep in mind that those overlap joints are going to need to be strong. The plane's all-up weight is 3 lbs. If you do a 4-g pull-up from an inside loop, that weight goes to 12 lbs. The standard safety factor for beams is 2.5, so that wing spar should be able to support 30 lbs to routinely survive serious aerobatics. And remember it has to work the other direction, too, if you're flying inverted or doing outside loops.
Rather than jointed PLA, it might be better to make a one-piece hollow wooden spar with an internal brace, all glued with high quality wood glue.
Good luck.