I would prefer to start with the Vickers Medium Mark I or II. They have front mounted engines and a rear door from the beginning. The hull, without turret has sufficient room for additional bodies. Raising the roof, if needed, is an easy change. It was tested in artillery, bridgelayer and artillery tractor versions. It will need a stronger engine and more armor.
Second generation on a lengthened Vickers 6 ton chassis, better front mounted engine engine, more armor and large box for the passengers.
It appears the only reason similar APC/IFV variants did not appear was money. Have a veteran of the trenches within Parliament start a campaign to ensure future soldiers are better prepared for war.
No reason you can't have both tracked and wheeled APC's, except will and money.