Turned it round - seems better.
Personally I would avoid the Chambers standard spring, they are not BSA ones but obviously sourced by Chambers from another spring manufacturer. They are quite soft and mine lost a lot of length after a small amount of use. I think the HW97 spring mentioned above is a good shout.
Plinkerer and Tinkerer
With a Mercury or an Airsporter it's a great help to do a dry build without the mainspring.
Rigger gloves or bare hands,you'll know the point or angle at which the trigger block and action threads engage.
Add a burly mechanic friend and the job's a doddle .