Sorry for the late reply, my draft seems to have gotten deleted. But as promised, here are some options I believe could be plausible for this tree.
A Portuguese portee combining a CCKW and a 25pdr, not sure if if this one is actually functional, but there does appear to be enough space for recoil compensation. 1.3-1.7 SPG
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A Portuguese Universal Carrier armed with a standard Boys AT rifle, but also what appears to be an MG13 on an AA mount. It will suck for sure, but I figured that it’s at least viable. 1.0 SPG
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A T-34-85 in Cypriot service, mounting an M1919 rather than an M2HB. I think it can work as a premium, trading the extra firepower for premium benefits. 5.7 Medium Tank
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A Nationalist Spanish (I think, judging by the Panzer I Breda in the background) T-26 with a peculiar modification; a roof-mounted MG 08. 1.0 Light Tank
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A Spanish project to implement the 105/26 Reinosa cannon on a StuG III chassis, known as the Obus Autopropulsado de 105 mm. Some sources say a prototype (of one of the two designs) was created with the leFH 18 howitzer as a placeholder. Further sources will be needed to confirm this though. 2.3-2.7
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A second Spanish ATGM vehicle based on the M41 chassis, and armed with the HCT turret containing four HOT missiles. I imagine you already know of this one, but considering that it was a direct competitor to the TUA version, I think it could be added anyways, perhaps as a premium or event. 9.0-9.3
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A near-prototype Spanish SPAA utilizing the Meroka CIWS system. Just recently, Tank Encyclopedia came out with a pretty detailed article on this weapon’s development and the attempts to get it onto an armored vehicle. The turret was intended for the ENASA 3560/02, a fire support prototype of the BMR 6x6 APC and a brother of the C.1 you have already added to the tree. It seems that at some point during the combination process, difficulties were encountered, and the Meroka variant (named the BMR-620) was scrapped.
In addition, the turret was combined with the AML-60 armored car, creating a functional prototype for test purposes. Either this or the BMR-620 would make for an interesting AA option in the tree.
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I also have a few more images and information regarding the Greek M113 (M61), not sure how much you left out from this post, but there is an improved model I will make a separate comment for.