2 main models of AMX 50 100mm exist to my knowledge.
The first one had elevated ventilators on top of the hull, like a Tiger/Panther. Plus, the tracks are resting on top of the wheels.
Second model has the ventilators directly integrated onto the top of the hull, and the tracks are suspended above the wheels by smaller ones.


You can also observe that the front of the hull is flat, and the gun mask for the 100mm cannon is fairly small.
You can clearly see the different ventilators on top of the hull, and a small step/difference of elevation between the turret position, and the rear of the hull.


I believe the second model with integrated ventilators is the most recent one, as the previous AMX 50 prototype under the name of M4 had elevated ventilators, and all the following models will have integrated ventilators. The same for the tracks.
AMX 50 120mm:
1st generation:
Realised using the second hull of the AMX 50 100mm prototypes, on which they installed a new turret with a 120mm cannon.
You can recognise it with the front of the hull, that is still flat, the step/difference of elevation between the turret position, and the rear of the hull.
Ventilation grids are on top of the hull.
Ventilators are integrated into the hull, unlike the first model of AMX 50 100mm
You can also observe the particular shape of the 120mm cannon's gun mask, that we will continue to see on the second generation, but not on the third. (letting us supposed that the canon got upgraded, even though all 3 models use 120mm shells.)
There is no ventilation grids on the side. (The detail will be important later)

http://www.worldweap... 50-120 (a).jpg
If you compare with the AMX 50 100mm, you can deduce this is an AMX 50 100 hull, as the front is still a flat plane & other details.
I also think that both AMX 50 100mm hull were converted to 120mm, but I have no proof. This would explain the mention of two AMX 50 120mm we sometimes hear about.
Front hull armor: 90mm
2nd generation: (Most probably the AMX 50 "uparmoured")
Top of the hull is flat. The difference of elevation has been removed.
Front of the hull is now edged/angular to deflect incoming shells
Ventilation grids are on top of the hull.

[We are actively looking for more photos of this model. If you have any, please send me a PM]
Front hull armor: Unknown
3rd generation: (AMX 50B, also called AMX 50 "lowered")
Top of the hull is flat.
Front of the hull is now perfectly smooth, and cast as one piece, making it more resistant than the usual welded pieces you find on the IS serie.
Ventilation is on the Side and rear of the hull.
The rear part of the hull is lowered, giving it a unique tracks shape.


Front hull armor: 80mm
This last model is known to have been tested with 4 different turrets. But only 3 are known to me:
T0B.120
TCB 120 (St Chalmont)
Turret D Side view, Front view. Looks very similar to T0B.120, but I think they are different ones. The lower rear part of the turret seems different. Turret D takes slightly less volume.