1947-54 Factory Assembly Manual indexes for Unison Seat and Cabs Seat Frame (Full Bench)
Unison Seat instruction index, RPO 264, Model All Cabs LD, Section 0, Sheet 4.01
Cabs Seat Frame instruction index, Model All, Section 1, Sheet 2.00
Check Attached photos
1929 - 1957 Chevrolet Master Parts & Accessories CatalogCab Seal Assembly - Exploded View
I'm not sure but I think the riser, under the seat, for the unison seat set-up is different than the Full Bench seat riser.