I did not trust the prescribed way of mounting the blocks. With a Saito 100 up front, I knew vibration would eventually loosen the block mounting and probably crack the Cowl. I Epoxied a 3/4 inch square of 1/8 inch lite ply to the inside of the fuselage where the block mounts. I drilled a hole through the spacer block so I could push a 4/40 hex head screw through the block. The hole is drilled in the rear half of the block. I drilled the start of the hole so that the head of the screw is counter sunk below the surface of the block. The screw goes through the block and fuselage and into a blind nut mounted in the 1/8 inch lite ply. I used epoxy where the block contacts the fuselage side (remove covering). Tighten it up and let the epoxy cure. When I mounted the Cowl, I put the mounting screw into the front half of the mounting block. Same treatment, both sides. Very secure mounting, and It has not vibrated loose.

I BUILD an ARF, I do not assemble it.