The muzzle brake looks odd on the 75mm, those were not common were they?
It's not a muzzle brake but a counterweight
It consists of two semi-circular weights that go around the muzzle of the gun, held together with two bolts on each side.
If you see an M3 medium with that, you can be sure it had a 75 mm gun M2 installed as well as a gyroscopic stabilisation system. This is because the stabiliser was designed for the 75 mm gun M3, which was the same as the M2 but had a longer barrel, so without the counterweight, the stabiliser would elevate the gun all the time if it was switched on.
The 37 mm gun in the turret could also have a stabiliser (and normally, if it was provided for one gun, it was for both), which you can recognise by looking for the counterweight under the gun. It looks like a pipe or a small gun barrel immediately below the 37 mm gun — like you can also see in the box art.
Building a Lee/Grant would be fun, it was an interesting design.
Some people think they're really ugly. I kind of like them, even though it was a very clunky design when you get down to it. I mean, whoever thought that putting the driver on top of the transmission, rather than alongside it, would be a good idea? (Answer: the designers of the M2 medium tank, which had a machine gun on every corner of the superstructure, so there was no room for the driver anywhere except in the center. Even then it seems a silly idea, but I guess they also wanted those machine guns high up to give a good field of fire.)
