Put the piston,mainspring and guide into the cylinder and then the cylinder sleeve. Make sure it is the right way round. Compress the spring and use a slave peg to locate and hold the sleeve. Keeping pressure on, you should be able to locate the cylinder screw/trigger pivot screw and push it through the trigger. Once located, replace the lock nut. Replace the trigger spring, making sure one end is on the TANG of the cylinder sleeve and the other is on its PIP on the trigger. Screw on cylinder end cap.
Locate breech block shims and place barrel in the jaws. Locate and screw home the pivot screw and the lock screw.
Locate cocking arm and replace its pivot and keeper screw.
Refit action in stock and replace the stock screws.

I think this is a nice little rifle. I was surprised at how good the internals were on mine. The piston washer was in good condition and the piston head screw retaining peg had no witness marks round it. I had a quick plink and it is accurate enough. The trigger has a long pull but is pleasant to use.

It is interesting to note that the German post war 25's had one pin to hold the sleeve and one to act as a trigger pivot. The British version just had one pin to do both jobs.