Positioned seat back hinge and seat forward hinge onto seat sling hinge halves to determine spacing on the rear cross-tie and the spar tunnel. Due to the lowered seat option, the hinge halves that will mount to the fuselage are a bit on the long side in that they almost hang over the edge of the upper crosstie and spar tunnel.
Drilled pilot holes in the upper seat back hinge half, then took off about 1/16" from the edge of the hinge to create a nice fit wilth the upper cross-tie.
Pilot drilled to the cross tie, then up-drilled.
Fabricated the two piano wire hinge pins by cutting to length and then bending the ends 90 degrees, 1/2" from the end of the pin.