77-80 grill interchange no problem, but look differant and vary do to differant options, trim levels etc. 76 is a one year only part. 73-75 are the deep dish ones. If you want to use a 73-75 in a 76-80 then you need to change the outer grill supports and use a 73-75 hood latch assembly.
The core/radiator support is the same 73-80 (except for 80 deluxe appearance package (square headlight) trucks), but may differ slightly because of options and have differant welded nut locations (differant cooling options, with or without a/c, 1 or 2 horns and wiring loom holder location). Some, ie very few, 77(?)-80 have an inside hood latch as option and have a differant core support as a result. BTW if you have an inside hood latch, the catch on the hood is differant also.
The lower filler piece is the same 73-78. The 79-80 (80 round headlights only) lower piece is the same physically, but has holes for the wider chrome trim. 2 mintes with a drill and a 79-80 chrome piece will fit on a 73-78 lower filler. The 1980 deluxe appearance package (square headlight) trucks) use their own lower filler.
Headlight surrounds will interchange 73-78 and 79-80 (80 round headlights only) but have differant painted/polish/non-polished inserts depending on year/options. The 1980 deluxe appearance package (square headlight) trucks) use their own headlight bezels.
The upper chrome piece is the same 73-80.
The lower chrome is the same 73-78 and 79-80 are the same, but wider.
73-80 turn lenses will interchange (except for 80 deluxe appearance package (square headlight) trucks), but 73-74's are orange with 1157 (clear) bulb, 75-80 are clear lenses with 1157A (amber) bulb. 73-78 may or may not have stainless trim, just depends on options. 79-80 (80 non-deluxe appearance package (square headlight) trucks) all take clear lense, no trim, 1157a (amber) bulb. The 1980 deluxe appearance package (square headlight) trucks) use their own turn lense which is clear and 1157a bulb.
The headlight harness will interchange 73-80 (80 non-deluxe appearance package (square headlight) trucks) but may differ slightly depending on year/options/loom holder location. The 1980 deluxe appearance package (square headlight) trucks) use their own wiring harness. The differance is the headlight plugs but will work with alittle fuss.
1980 deluxe appearance package (square headlight) trucks are basicly their own cookie. But the complete package (core support, wiring harness, headligts, turn lenses, lower filler piece etc) will work in any 73-80 truck with round headlights.
Now if you have a 1980 deluxe appearance package (square headlight) truck and don't like it, you can change over to the round headlights with just changing the bezels, lower filler, headlight buckets and complete turn lense assembly. I should note that SOME 80 round headlight trucks HAD both set of holes for both round and square headlights. BUT I am unsure if these were deluxe appearance trucks that were changed to round headlights or GM just used what they had when they assembled the trucks new. I have personlly have changed 3 80 square headligh trucks over to round healights do to the unavailablity of square headlight parts.
The square headlight (deluxe appearance package) was availble on all 1980 trucks blazers and suburbans. You could have a plain jane custom deluxe truck and still get the square headlights. ALSO it is possible to have a hard loaded Silverado and delete the square headlight option. I have had one of those trucks and could verify its history, but it is in no way common.
While we are on frontends...
The inner fenders are basicly the same 73-80. But these vary alittle do to options. With or without jacks, jack tools, with or without heater (fyi, heater trucks have an extra hole for the heater hose holder), single or dual batteries etc.
The fenders are basicly the same between 73-80. Back in the day, there was actually 2 fenders, one plain jain and one with the common stainless strips. The stainless strip fenders had factory holes for the metal clips that held the stainless trim on. The later fender was discontinued as soon as the 81's were being built.
The hoods fit 73-78 and 79-80. The 73-78's were flat accoss the front and the 79-80's had the rasied portion alon the front. The 73-78 hood will replace the 79-80 or 79-80 will replace 73-78. As far as I know, the 73-78 hood was discontinued as soon as the 79's were being built. Trucks with factory hood emblem of course had holes for that...
