Very interesting idea with the M4A3 (90) HVSS with T26 turret on the M4A3E2 “Jumbo” hull. First time, I see this drawing.
When I first saw the picture of the M4-based proposal with the T-26 turret, my mind began to wander (it does sometimes, and I live with it 
).
To gild the lily a bit further, these additions to the M4A3E2 based variant would also have been possible around late 1944/early 1945.
- slat armour to counter handheld HEAT weapons like the Panzerfaust. Think Strykers in Iraq or Afghanistan.
- a large turret box to hold all the crew gear (tankers never have enough room for their gear). The one from the Canadian Leopard 1C2 is shown just because, it is huge in relation to the turret.
- the longest barrel variant of the 90mm (M3?)
These features on the M4A3E2 hull with HVSS.
I came very close to actually starting this project, but another “What if” project took my attention in the end: Hypothetical - what if M103A2 in service with the IDF - Israeli Defence Force
The real life spoiler to this happening would of course have been lack of engine power. The 500 HP Ford engine of the M4A3E2 was already to small to fit the task, so an uprated or different engine would have been needed