Hi, trigger adjustment is by way, as you say, of the hi-lo screw set. looking at the breech block from the side with the stamped markings the rear hole has two screws in from opposite sides.
From the left (as you aim the gun as normal) the screw has a tapered shaft and flat end, from the right goes the lock screw, which has a flat end. The system works in a basic way in that the taper portion of the screw bears against the trigger and effectively "pulls" it, ie. dis-engages it with the sear as the screw goes further in. Once you are happy with the pull, the opposite screw is tightened which jams against it to prevent movement. Use two screwdrivers for precise adjustment, ie. to prevent the hi-low screw moving whilst you tighten the lock screw.
John Knibbs has these showing on his website at £8.50 per screw, ie £17 plus postage the set....
I may (will check later) have a set here...will update.
trigger / sear layout here;
http://www.flickr.com/photos/3122848...-7Aep9k-82G8ch
Note;...Do not go too light on the pull weight, as this can cause an unsafe gun with the possibility of both an N.D., and serious damage to the sear, which is prone to crack if very little overlap is created.
Also...Check piston rod for movement in piston, and pull piston to rear of cylinder and check for play as these can be an issue if you start trying to get a light pull off.
Lowest safe weight, with trigger and sear engagement faces in mint condition, all pivots good, and a solid and VGC notch area piston rod, is about 2 1/2 pounds...normally the factory set these around 4 pounds, and if ANY doubt stay around this figure...buy a low range spring balance like fishermen use, and bend the hook or rig up something to allow accurate measurement to prevent tears and expense
ATB, ED