I've only ever seen these on diesels. My 84 and 86 6.9 F250 supercabs both have them but none of the gas trucks do. Same story in the jy. Did they come on gas trucks?
Scott
'Camano' 1986 F250 Supercab XLT Lariat 460/C6
'Chanute' 1980 F350 C&C 400/NP 435 - Gin Pole