Thanks for the good words about me and my products
Just what years are you referring to as 'later trucks'?
It sounds to me like the cab was replaced at some time. The frame is drfinitely a K series frame. Compare the cab VIN to the frame VIN.
Sorry I can't help with the hood grills, I've only had a couple '60-'61 hoods in my time and I don't remember what was on the inside.