Baron I m not trying to argue with you
I am simply researching this now as it has me curious . From what I see online it seems to be a late model 77-79
78 is when the grill changed , but it is listed on a few sites by the number that was given by Mike Files as a 77-79. this is the other info I found.
http://www.cardomain.com/memberpage/278209
The Impala “S” model and Sport Sedans were dropped. All models had pillars. Impalas had an 8 x 3 hole eggcrate grille pattern with center Bowtie emblem, plus quad rectangular headlamps over quad park/signal lamps. The new Impalas were shorter in length, taller in stature and narrower. Impala embodied the new image of the full-size American car - smaller, lighter, more efficient. (For example, even with its trim dimensions, the new Impala featured increased headroom, legroom and trunk space.) The formula seemed to work. All-time sales passed the 12-million mark. The Impala had adapted once again. The 1977 Impala/Caprice was a style leader
1978 brought about few changes except for front and rear styling treatments. The Impala carried a new horizontal-bar grille with a Bowtie above rather than on the grille itself.
I do not own a 77-79 impala nor have I ever , so I can not agree or dispute first hand. All I knwo is it isn't a truck grille