My '51 has the rod (no pulley system), my '50 COE does not have a rod(with pulley system). I think on the '50 the only detent is on the driver's side at the adjuster lever.
Jim Carter lists "seat adjusting rod anti-rattler grommet, CB153" only for the years 51-55, implying there was no rod before 1951.
Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix