Ash +1
Tarvis, people who sell them often bastardize the actual Ruger descriptions.
For the collector there are really only two variants that are important...and a whole bunch that should be left behind. But before I get to those, some important background information. For many years, for decades, Ruger held a very stern view of civilian sales of any of their government/military products. Whether it was firearms or accessories, if it was at all mil/gov, they banned their sales and really aggressively went after dealers that sold them to the public...
Only in the last 5-6 years have some cracks come through the wall, having mostly to do with the death of Bill. For instance, it is a well known fact the old man Ruger was not an advocate of U.S. citizens buying high capacity mags from anybody, let alond Ruger. Collectors sought out the high capacity early Mini14 mags with relish.
Now the GB.
The most important variants have three major characteristics. First, they should have the Ruger factory swing stock. Secondly, they must have the Ruger factory barrel band/bayonet rear lug and factory bayo flash hider and thirdly they should be the units packed with the high capacity factory mag.
Know that the GBs came in two major receiver configurations...integral scope mounts and without integral scope mounts. A number of collectors feel that the paramount collectibale GB is....the stainless steel, swing stock, NO integral scope mount, bayonet lug (always in blue steel) and flash hider in the earliest model run that can be had, with the high capacity mag. IF you can find one LE marked...more the better. I personally think the blued model (same configuration) is very collectable. I am not dissing the full stock, they are collectable as well.
AC556 is still a holy grail of US manufactured Class III and it was and is hard to track them down.
Where things turn south quickly for value is...any synthetic stock...anything without the bayonet lug.