Hi Chris,
I'm sorry if I'm being dumb

I understand that you have a William b.1821 to Samuel and Elizabeth but I still don't know why you think he is definitely George's father.
I think that the fact that he is a die sinker in 1841 seems to make him more likely to be the William married to Caroline in 1851 and 1861.
In 1851 William and Caroline are living in York St. Harborne, Staffordshire next door to John and Rebecca POWELL. In 1861 an Elizabeth READING Mother-in-Law is living with John and Rebecca POWELL still in York St. Harborne, Staffordshire. If Rebecca is the daughter of Samuel and Elizabeth READING then doesn't it seem more likely that the William READING next door in 1851 is her brother rather than another random William READING.
Possible marriages for William and Caroline are,
William READING Dec Q 1845 King's Norton 18 559
Caroline BENNETT with same details.
William READING Dec Q 1847 Birmingham 16 535
Caroline KIRK with the same details.
If I were you I would get the above certificates to check who those William's fathers were, just to make sure. Harborne was in Kings Norton Registration district so I think that's the most likely.
The William b. Canterbury and Ellen that I found are living in Allison Street in 1851 doesn't that make them more likely to be George's parents?
I hardly like to suggest it, as I understand from experience how frustrating and upsetting it can be to find you have followed the wrong line, especially if alot of time and effort has gone into the search, but I always think it's better to be sure.
Please don't shoot the messenger, my thoughts could be wrong
Regards,
Daisy