Welcome to the world of having an idea what tank soldiering was like!
As I already mentioned somewhere else on here; you ideally needed to be short, slim, wirey and have universal joints for wrists and even ankles at times (prone to getting caught when the turret traversed relative to the hull and you had to watch out for your feet.
I'm not old enough to be familiar with the Comet, but knew the Charioteer (Comet Hull with 20-pounder box shaped turret). Even the Cent(urion) which was positively roomy in comparison was not for anyone taller than say 5' 9'' and anything more than a modest girth.
The Chieftain wasn't much better; worse in some respects. But at least they both had a Boiling Vessel (BV)!
That Comet doesn't even have the 17-pounder fitted which used a much longer cartridge case, so even less interior room.
The Brits were not even issued with head protection, just a beret.