Hello Kev.
Although I have no experience of the S models I do know enough about the earlier models to give some advice. I have to remove the cocking assembly. There is one large pin where the cocking lever pivots on the trigger block and I separate the cocking slide connecting link from the cocking slide by removing the smaller pin where the two join. You can then simply jiggle the slide out.
No doubt others can help with the trigger block and the maxi grip rail.
I have fitted three Welsh Willy kits to Airsporter/Mercurys and can vouch that they come pre cut to a length that makes fitting the trigger block much much easier.
Have you looked up Pellets and Pistons on you tube? Because I am certain that I watched one of his videos on a Stutzen which might help you.
ATB DFL
The more I think I know, the more I realise the less I know.