Doesn't the speedo cable attach differently to the earlier version? Easy fix, technically, by using the proper speedo cable pieces, but just something to be aware of. That little wire bit coming out of your lower cluster's speedo looks like the speed buffer "eye" that counts the revolutions of the speedometer cutter wheel for use in the CCC system. Obviously won't be needed on your 79, so that's a moot point. Honestly I've never swapped an older cluster to a newer G, or vice-versa. It appears it should work, maybe. Only one way to find out.
As pointed out, there are some little differences in the faces of the gages.
For the U.S., speedometer faces were different on 78-79 as they were just MPH. 1980 added the km in dark orange-y color. Then 81 used a "light blue-ish" km inside the MPH. In 1982-88, the speedo was the same (exception was 87 442 120 mph only).
Tachs- 78-79 were the same, then a slightly different font was used for 80, and then again for 81. 80 and 81 are technically stand alone years, believe it or not, for speedos/tachs. Starting in 1982-88, the tach faces were the same. Caveat: Column shift cars with gage package and 83/84
H/O has a lower plate on the tach that contains the needle and shift indicator lettering (H/Os don't have the console indicator light up at night). Has nothing to do with the tach proper, but if you see a gage cluster with the lettering and you don't need it, it's not a big deal. The plates can be swapped out, or modified if need be. All the gage clusters have the ability to accomodate the shift indicator setup.
One more tidbit about tachs. Up through I believe it was 85 or 86, the tachs had a V8 or V6 orange jumper plug in the back of them, which usually would loosen up over time and cause the tach to read weird. Fix was to solder a jumper piece wire across them. By 87 for sure, could have been 86, can't recall specifically, the cars were built with the jumper wire soldered in from the factory and no jumper plug.
For the "little gages"- the fuel/oil , etc., gages looked the same from 78-80 and between 81-88 as they added the universal indicator symbols on them in 81. Also, it's slight, but the 81-88 volt meter warning area is less than around the 12 V area, where the 78-80 has anything less than 13 V in the warning zone. Weird.
BTW, to add, your top cluster has the appearance of the 78-79 faces, the bottom one has the appearance of 82-88 column shift car.
