One way you might just get it is if development time and resources weren't wasted on designs that never got anywhere.
Peter Beale's 'Death by Design' lists the following which took up design time and effort.
A23, A26 and A43 based on the Churchill
A33, A37, A38 and A39 Assault Tanks
A28, A29, A31, A32 and A35 based on the Centaur/Cromwell series
So, drop the Assault tanks (if you really want one, base it on your A41 Centurion), anything based on the Churchill, use the Cromwell as an interim measure and shoot TOG.
For the gun -
http://www.wwiiequipment.com/index....er-anti-tank-gun&catid=40:anti-tank&Itemid=58
The Ordnance Board was also asked to provide solutions for 80, 90 and 100mm, the board recommended a 20lb shot of 3.45" calibre, the same as the 25pdr but a piece more like the 3.7" AA gun, this requirement was dropped in March 1940.
For an engine, well the 500hp Thornycroft RY12 keeps popping up as a possible tank engine from the late 1920's all the way to 1939. I've never seem anything to say why it wasn't used operationally.