I usually use an O ring in the front grove and leave the ptfe one in the back (for lube I guess). I also have found Bsa Meteor (Mk1-Mk5) mainsprings are a better fit in Hawks/Ospreys etc. I have never gotten round to having a proper guide made up, but I am sure it would improve things. I do away with the ratchet and the safety and use a sear spring from a Victor, polish the mating surfaces of the trigger and sear a little and take a few coils off the trigger spring or find a slightly softer spring (NOT A BIRO ONE!).
One idea that I might get round to at some point is to either (1) Drill and tap the end of the piston and fit a leather washer, which would short stroke it (2) get a bit taken off the end of the piston and fit a leather washer. I havea feeling that with the mods, something doing a fairly smooth 9.5 ft lbs would probably be the ideal.
My rough Hawk Mk3 (Bloody neighbour still has it as he borrowed it to get a few rats in the garden) has the Meteor spring,1 O ring +1 ptfe ring and the trigger mods and shoots quite nicely at 9.5ftlbs but with quite a fast firing cycle. It is one on the guns that everybody seems to be able to use ok.
The trigger blade still feel awful as do all those Webley ones, but it is a good trigger.