one of a Zis-5 3k kv-1 prototype http://tankarchives.blogspot.co.uk/2014 ... 5-3-k.html


And one with a t-34 57mm prototype;https://panzerserra.blogspot.co.uk/2014 ... eport.html


I am going to use these to make an educated guess at the mantlet's shape which appears to have a cutout around the mantlet gun port.