A little tweaking, but honestly the cupola was the only thing I could think about that needed adding. The Ersatz Panther would make a good alternate design for the US Army in TL-191 I feel! Could go up against the Confederate's heavier barrels honestly.
I actually think the "Ersatz" should be its own medium/heavy tank. The M7 Custer ("Armstrong") ones that you made, the ones with the PT-76 like turret - those I think you should keep as the Custer, while the "Ersatz" can be its own model - by American standards it would be a heavy tank I believe, while the Custer you made would be a medium. Plus, I don't think the US Army would have a tank like your Ersatz at the beginning of the war considering how lethargic the Army was in developing good tanks post-Great War. So the as of unnamed Ersatz can be a mid to late war design to combat the heavier tanks the CS Army has.
Still want to name it the Roosevelt btw, to name any tank the "Roosevelt" but I'm alone on that
Oh well.
Yeah baby, this one looks nice! Actaully this one could be a good mid-war going to late-war model to me, similar development in mind to the T-34-85. Like, if the original M7 Custer was the T-34-1941/1942, then the up-gunned one you made here would be the T-34-85 equivalent, if that makes sense. Or if yo want to use American tanks - this one would be the equivalent to the "Easy-Eight" Sherman.
The gun on it looks sufficiently powerful too! The added tweaks I can see as being upgrades to what crewmen said needed fixing.
I vote to keep the name "Custer" for it honestly. The "Custer" family of tanks!