Actually its not just common- it was on EVERY NON SS ELCAMINO.... 1968-69 that is.
68-69 Elcamino's Unless they were SS396's got that malibu trim peice above the glove box. SS cars got one that said SS396 (duh)
That guys ad is flat out wrong about the years- that trim peice(or even the SS396 one) was only used in 68-69 not in 70-72. And actually 68-69 had slightly different ones for each year. That one looks to be from a 69.
And back to the Malibu thing... Actually in 1968, elcaminos could even have Malibu trim tags on the outside of the car, i have seen several of them, they don't say elcamino anywhere on them, just Malibu badges- and it is correct!