Okay..in an attempt to clear all this up....or to further confuse....
The official parts books seem to show:
The dogbone for '73-'78 is Fiat # 4338203 which supercedes to 4437613
The dogbone for '79 up to 12/79 is 4437613
The dogbone for 12/79 on is 4468878 ( 12/79 would be halfway though the 1980 model year )
It is not clear to me which dogbone a 12/79 would take....
So it appears to me that there are 2 different dogbones....and is NOT a 1300 vs 1500 thing.
At the exact same time ( 12/79) that the change occurred....there was also a change in the upper chassis member that the dogbone bolted to. Which would lead me to surmise that....that mounting location is now further back away from the engine ! And thus required a longer dogbone to keep the top of the engine in the same location as before ( none of the other mounts or chassis bits changed at the same time )
The upper ( horizontal ) part of that chassis did not change at that time...only the lower ( vertical ) part of that member ( they are 2 separately available pressings ). Which would seem to mean that....either the vertical part of that member is now further back.....or more likely that the bracket that protrudes from it is now extended not as much.....
Our trusted faithful vendors seem to be at odds about all this.
Vendor "O" states that 4338203 and 4437613 are indeed the same and are 131mm long ( centre to centre ) and was used on all 1300s and 1500s up to 12/79. And that 4468878 is 153mm long and used from 1/80 on...
Vendor "E' states that all 1300s and 1500s up to 12/79 used a 134mm dogbone and from 12/79 on used a 147mm . And state the difference is due to that chassis bracket being "more extended" on the early models.
Vendor "V' states that all 1300s took a 137mm dogbone and all 1500s took a 148mm
Vendor "M" states all 1300s took the 4437613 132mm dogbone...and all 1500s took a 4468878 145mm dogbone
Quite a difference of opinions !!!!
I tend to believe the Fiat parts books and vendors O and E..
The controversy here seems to all about the early 1500 models. All the '79s and halfway into the '80 model year..
I reckon...a good approach would be to actually get some real life measurements for some 1500 models. To settle this once and for all..
I myself actually tend to believe that indeed there was a chassis change in 12/79. Most likely in the distance that bracket protruded from the vertical part of the upper chassis member.
Below is a pic of my late '81:
You can see the bracket for the dogbone protruding out.
Under that top horizontal portion.....the vertical part of the member is recessed 1/2" from the front lip
The centre of the mounting hole for the dogbone is 13/16" out from the recessed vertical part. This seems to agree with Carl's ( '83) measured 21mm.
This mounting hole is about 1 3/4" lower than the lip above.
I'm betting that 13/16" measurement is considerably more on a '79 model. Now if we could only find someone with a '79 to measure and confirm. Larry...you are now up to bat........