Ps. I need to send forum member Josie & John a message with the trigger/trigger block compatibility question.
This is where I read about the three trigger types:
http://www.airgunbbs.com/showthread....Trigger-weight

Josie & John writes:
"Hi,

You can adjust it. There were three types of trigger on the Mk III. The first was the so called double pull with adjustment screw located on the trigger blade. The second and third had a locking screw on the side of the trigger block, whilst the adjusting screw was located on top of the block. The differences between the 2nd and 3rd types is the 2nd has a curly trigger profile, whilst the 3rd type has a shorter trigger blade, which sits slightly further back. The 2nd type had the best and 'crispiest' pull, whilst the 3rd type probably had the heaviest pull. Ironically the Supertargets were fitted with the 3rd type, which in my experience was the worst trigger on any of the Mk III rifles!

As a rough guide, the 1st type can be seen on rifles serial numbered to 6000. The 2nd type from SN 6001 until the A prefix was introduced in 1966 and the 3rd type on letter prefixed rifles.

John"