I think the bomb is an 8,000lb one.
The basic model was a 4,000lb cookie with additional modules bolted to create a 12,000lb one. I once read a secret report (translation) of a Luftwaffe report on the 12,000lb bomb. It was interesting as they credited it with a laydown capability with parachutes and a high level capability with the streamlined tail. In otherwords they didn't seem to realise that the Tallboy and Cookie were two different bombs.
At East Kirkby they have examples of the cookie, Tallboy and Grand Slam. I seem to remember two are the real bombs and one is a wood and canvas mockup. IIRC it the the Grand Slam that is the mockup.
As for the two holes in the perspex, present in Just Jane and absent in G-George, I think they may be for ventilation. It could get very hot in the nose in summer and also condensation in high humidity. I don't know when that was done. Lots of the transparencies are new.
At one airshow, after I had broken the Astro Dome, this chap came up and asked about the perspex. He then said he owned a plastics company and offered to make a complete new set of transparencies. Come the annual maintenance he took the orginals and made a splendid set of new ones. I suspect the Pantons have been able to get new ones as well.