John Walter "The Airgun Book" (1ed. Blue book p.105, & 4ed. p.99).
Peter Bower's "Meet Your Match" article (AGW Nov 1980 p.31) is another source.
The very first MU's in the UK (May 80 >) had 3, subsequently 2, until the second variant was introduced in 1983.
The second variant's spacer system also employed cams which allowed lateral movement of cheek piece.
Here's a couple of (low quality!) photos of a 1981 Match Universal showing the 2 piece config, in position and removed.
The top line of the butt is fully flat to the recoil pad in the second variant, unlike the earlier model, which makes it easy to tell them apart even from a distance.
It's not impossible that some retailers only offered the additional pieces as an option, but generally they should have been supplied along with the raiser blocks.
I totally agree that the LGR is a great rifle, I've got one and sold my FWB. Although Barry Dagger did ok with his 300s at the 1984 Olympics, and the last springer to win a major championship was an Anschutz 380 in 1984, the sledge design perfected?
The Walther's do require a bit more effort to cock than the springers, and some buyers want a little more velocity for posh plinking, mini-sniping etc which is fairly easy to achieve with the springers, hence IME they command higher prices despite lacking the Walther's luxury quality and technical superiority.
Hope that all makes sense. It's always risky giving valuations as people can take offence, but if we only ever tell people what they want to hear it's all a bit pointless even asking the question.
Hopefully the OP will edit the thread as it'd be a shame for it all to get deleted for inviting offers, especially after typing all the above.