Need help Centering SMLE barrel (trigger guard issue?)

[30Three]

Looking at your very first photo, it appears that it's the receiver that is off centre; not just the magazine catch. The gaps between the receiver and wood are not equal.
Are you sure of the fit in this area?
I am not an expert; but I did deal with a similar issue on my no1MkIII*. In my case the selling dealer had attached NOS woodwork to the rifle without correct fitting. The rifle shot a 6" spread at 50 metres.
To correct the issue I started by reading as much information from experienced sources; such as Capt' Peter Laidler. Only then did I strip-down and examine the rifle.
How did you ensure equal load on both draws? In my case there were several issues with the fore end; but the cause of the barrel being off centre in the barrel channel was corrected with proper adjustment at the draws.