That’s really tricky, in the first it’s something familar, but on the second look:
It’s not a Semovente, not a Vickers not a Japanese or Czech or Hungarian.
I suspect the British, but I need a hint:roll:
A Czech Marder with pierced armour design… There… I guessed. 
So sorry for my protracted silence, honorable ladies and gentlemen! Unfortunately, I was beleaguered with my current professional obligations at the International Book Fair in Belgrade, but I think that very soon I will be able to serve you in full capacity.
And no, my dear Mr. Prime Minister – this is not a Czechoslovakian vehicle. However, I am taking the liberty to draw your attention to an almost incredible, but very important fact: this vehicle has the engine compartment at the front of the chassis! 
Israeli.
have at it
JS-3.
The other one seems Israeli to me…
Israeli self-propelled gun, produced in the WW2? :shock:
Alas, my dear Mr. Prime Minister, that kind of a… rarity is completely out of this world. :roll:
I’m just saying things…
Italian 90/53 Self-Propelled Gun.
Could it be one of the many Waffenträger prototypes?
Actually it’s an IS-3.
If you want to be that exact it would be ИС-3. Both designation are used in western countries: IS = Iosif Stalin, JS = Joseph Stalin.
lol
Italian 90/53 Self-Propelled Gun.
You mean Semovente 90/53, my dear Mr. Prime Minister? Well, this proposal of yours surely is a significant improvement in your analytic approach, however, your suggestion is still suffering from a deliberation fatigue.
First of all, our cannon evidently has a double-baffled muzzle brake, whereas Italian solution is not equipped with this recoil-reducing device. Furthermore, Italian vehicle has only three top rollers, whereas our mystery machine has four rollers beneath the track. However, I have to admit that this suggestion of yours is much more suitable than that previously mentioned one. Please – carry on! You are obviously on the right track.
Could it be one of the many Waffenträger prototypes?
No, my dear Mr. Kamehouse. Our vehicle is not connected with Germany.
Hm…
Sorry, no idea.
Can you give a hint, please?
Of course, my dear Mr. Tom: our machine was equipped with the 3.2 liters, one-piece-casted L-head petrol V 8 engine produced by Ford and capable to set free astonishing 85 HP! 
This is an Cañón Autopropulsado de 75/40 мм. “Verdaja”.
Exactly, my dear Mr. Sergej - Pieza Artillería autopropulsada de 75/40 mm Verdeja-I.
Bravo!
That was a long search.
My offer: Yes the chassis is well-known
but what is the strange stuff on it?
Maybe a poison gas attack tank. The cones have lights in them, and the long tubes have a poison gas in them, to be detonated behind enemy lines…
Very good!
The gas isn’t poisonous but you are definitely on the right track.