Since the TB aft corners have a slight curvature to it, it was a bit difficult to shape the foam for a good fit. Here's what I did...
I taped a strip of fine sand paper (6"x10") along the aft end of the TB. I took a chunk of scrap urethane foam and rubbed against it (up/down and rotation motion) until the corner of the foam conforms to the aft corner of the TB. Then I removed the sand paper and did a final shaping and trial fit on the foam with some slight touches.
Once completed, I took a razor blade and trimmed the foam block to the triangular shape per plan. My triangles turned out to be ~5" long on both sides - so that they look symmetrical.
I microed the foam wedges in place per plan and made up 10 6"x12" BIDs for the engine mount reinforcement. Due to all the odd surfaces and edges at the corners, I expected challenges in getting the BID to lay down nicely. Therefore, I took time to smooth out all the corners and wedges with sanding and micro before hand. In addition, I wetted out all the BIDS separately, then laid them down one at a time. Less challenging than expected and they turned out nicely. I peel-plied both sides and let cure overnight.
The 8 ply lay-up looks challenging at first. However, if you plan it out ahead of time - it turned out relatively simple. I cut out a paper template shaped like a letter L. The width of the L is 4" wide, with one arm 12" long while the other 10". If you arrange your 'L' shape glass elbow-from-elbow, you'll end up with a 12" x 14" rectangle. If you line them up at 45o on the BID, you will end up with 3 rectangles or 6 L shape plies per 12" strip of BID. Actually I just cut a 12" wide BID at 45o, pre-wet it like a BID tape. Then I marked out the 'L' shapes on the plastic, trimmed and lay them up one at a time.
[Hindsight] This may not be a good idea after all (see below).
[Hindsight] When I read the Plan instruction, I did not get the impression that the BID should be a single continuous layer. That's why I went with the L shape glass (above). This approach was brought up in the Cozy forum a few days ago and it was pointed out that my approach will have a seam (disconnect between the turtle back and the spar surface (as show in picture left).
I did not follow the plan dimensions when making the aluminum hard point because my engine mount hard points (Chapter 4) are round discs w/ 1.75" in diameter. I just measured the appropriate dimension such that the aluminum hard point covers the entire disc and fits against the sides of the spar and the TB. I did not taper the sides of the hard points either because the tapered edges will not be useful surfaces for bolting, thus limiting the useful size of the disc on the back side. Instead, I just packed the sides of the aluminum inserts with flox and lay-up the 1 ply of BID over it per plan.