He was always one to be underestimated, as The Crowned Prime Minister showed.
I still have a shock, in a good way, when I see people use my TLs in such a context.
Anyway, I am interested to see where this will go. George Brown, like Roy Jenkins in my mind, is one of those people who you need to feel a relation to on a personal level to have less of a hard time getting over his many flaws and issues, which I lacked so his mannerisms tended to push me towards the dislike camp, although your TL might work to show that his positives could outweigh the negatives. The immediate butterflies will be interesting, especially in another leadership contest that has yet to be mentioned by some.
IIRC Brown was in favour of keeping away from the Profumo Affair, in contrast to Wilson's OTL stance, which could lighten the load on pressure weighing down on Macmillan. On the other hand, there were a few in the party who rallied to him during the crisis despite the policy troubles in multiple other areas, so whether he goes to get his health checked at around the same moment as OTL is a fair question. If he catches his regular doctor, we could see Macmillan staying on long enough to lose to Brown in 1964.
Assuming he resigns, whether by the same or different circumstances, the leader after will be interesting. Home's rise wasn't guaranteed after all, as Hailsham's photo with his daughter could be butterflyed, or Macmillan and the grandees aren't scared off by the intense support the base had, or you literally could have Rab Butler fire the gun when it was placed in his hand. Butler's plan was to promote young men like Macleod (who hated Jenkins and Wilson, and was fond of Callaghan) and Powell, and I imagine Brown has high places designed for Woy, so we may see the two face-off just like IOTL. Unlikely, as Butler imagined Number 11, and a jump to Shadow Chancellor may be too much, even for a character like George Brown.
All in all, I'm on the edge of my seat and can't wait for more.