feetupfun

That hub did not come with a chrome lining. Later Bultaco hubs did have a chrome lining
Like every other drum brake, just because the pieces are all in place, it doesn't necessarily mean it will perform well
Even if everything is perfectly set up perfectly in that particular hub, it will not work as well as many other twinshock trials bike front brakes, so don't get excited about it ever working strongly.
 
As with all drum brakes, here are the things that need to be done right for it to work as well as it can:
The drum surface needs to be smooth (shiny)
The drum surface needs to be concentric with the axle
The drum surface needs to be parallel with the axle
The drum surface needs to be clean
The curvature of the show friction material needs to perfectly match the curvature of the drum
The outer surface of the friction material needs to be concentric with the drum surface
The friction material needs to be of modern composition and designed for the purpose
The friction material needs to be bedded in (smooth) and clean
The wheel bearing races need to have minimal running clearance
The bearings need to be solidly mounted in the hub
The axle needs to be installed so that the friction material is centralised in the hub
The camshaft needs to have minimal clearance in its bearing
The cam needs to be almost flat against the shoe pads as the friction material touches the drum
The camshaft arm needs to be at 90 degrees to the cable inner as the shoes touch the drum
The cable outer needs to be kink-free and clean inside
The cable inner needs to be kink-free and lubricated
The camshaft lever needs to be the right length
The handlebar lever needs to have the correct leverage ratio and be free-moving
 
There are businesses that can do the relining and machining of the shoes and drum for you
 
A common mod for Sherpa T front brakes is to fit the front hub or front wheel from an Alpina from M115 onwards or from a Frontera. They have bigger brakes that work well, but being bigger, do have a slight weight penalty. Alpina front wheels are commonly available on eBay. They look like the later model Sherpa T front hub. Most people would not tell the difference unless they were side-by-side. I can post a photo if you want