Just out of interest, and maybe not so easy to answer.......
my ferret has the regular appliqué armour at the front of turret and hull, but also has reinforcing gussets at the wheel stations and also extra metal welded on the belly.
i am guessing this is a retrofit as the bins appear to have been bashed on the inside to enable the gussets to fit. There is also one bolt missing on each wheel station, which I have been told was done to create a weak spot in case of mine damage.
so, what mark is the ferret? Is it just an up armoured 2/3, or is it a 2/4? It came off the line in 1959, so not a particularity early one.
cheers
mick