Sorry guys. The part was used on the filming miniature of Slave I for Empire Strikes Back. So, it's likely to be from a kit from the later '70s. It was repurposed as the gun turret base and appears on both sides of the hull turret section (aka., elephant trunk). The cannon's themselves are from the M-42 tank.
Beyond that I have no idea. And, I've looked at a lot of kits. It appears that the part has been cut, as indicated in the pic below with the red lines and the notched section on the opposite side is possibly cut, too. Some of the pics from the side seem to have indications that putty was used. The part shaded in blue probably isn't related. Probably.
It doesn't seem to be from any armor kits. Cars are a strong possibility, or motorcycles... Just not sure.
It's been reported on the Replica Prop Forum that a member there has identified most of the parts. From what I understand, he is missing a few pieces located beneath the 20mm Flakvierling part on the tail end of the undercarriage where photo-reference is not available.
I have messaged with him a few times, and he provided help on one other part. For reasons not entirely known to me, he has elected not to share any additional information. Studio Scale parts identification is a somewhat contentious subject and people don't like sharing information for a variety of reasons. To be fair, I don't have anyinformation to offer him in return on Slave as I don't have the pieces from the tail end of the undercarriage, either.
There is a group of 4-5 of us that has collaboratively identified about 95% of all the parts used on Slave. Possibly somewhat more than that. This particular part that makes up the cannon turret is one of the few remaining pieces that we have yet to identify.
I posted here on the off chance that someone would recognize the part, since there's a broader range of modeling interests represented on this forum.