First off, thanks for supporting SSBC and bidding on that rod in the auction. Sounds as though it ended up in good hands. As mentioned above, it is a truly rare blank and a pretty cool addition to any centerpinners's collection. To your questions:
I wouldn't bother contacting Sage on this one. It is such a rare model that I think you would be hard pressed to find anyone that was around when this rod was made. There's probably one guy in R&D that would know a bit but you probably won't be able to get through to him. Sage is first and foremost a fly rod company and the Gear end of things has pretty much been turned over to me now. With that in mind, I'll do my best to give you some info.
4106LLB: 10'6" power 4 Light Line Blank
* Made for approx. 4 years back in the 90's as I recall.
* Simply didn't sell enough numbers to stay in the line-up. This was back in the day when powerful, 10'6" slow action (fiberglass was still popular) rods with 4" Silex reels loaded with 20 lbs Ultragreen line ruled the river. A rod like the 4106LL was very different from what was the popular choice. Nonetheless, those who took a chance with this rod, fell in love with it. A bit ahead of it's time.
* Back then Sage offered the following 10'6'' blanks as best as memory serves me: 1106LL, 2106LL, 4106LL, 2106L, 3106L, 2106, 3106
* The best way to explain the differences would be to categorize the 2106 & 3106 as "fast" action where most of the deflection occurs in the top third of the rod making them suitable for levelwinds. The 2106L & 3106L were "moderate" action with most of the deflection in the top two thirds of the rod making them suitable for centerpins. The 4106LL, 2106LL, & 1106LL pretty much bend right through the cork and are also suitable for centerpin use - especially with lighter line and less external weight.
* Within each of these series there are different "powers" - 4,3,2,1,etc.... This is exactly what you would expect in that a 4 is stronger or more powerful than a 1.
* Line rating is a very subjective thing. It is mentioned above that this rod rates 4 - 8 lbs. I happen to reccomend 10 - 14. Neither is right or wrong. Put it this way, that rod will cast 4 lbs line or 14 lbs line quite nicely and will handle fish to 20 lbs no problem. Use what you're comfortable with.
* The blank itself was made with Graphite ll. This was pretty cutting edge in the day. In the current Sage Gear line-up, most blanks are utilizing Graphite l with the exception of a few of the shorter casting rods like the CT290F for example which utilizes Graphite lll. Graphite ll is a higher modulas than Graphite l. You should notice that this 4106LL will be physically lighter than your 2106L.
That's about all I can think of right now. Hopefully this answers some of your questions. Somewhere in my files I actually have a Sage blank catalogue from back in those days. If I can dig it up, I'll scan and post it. There was some interesting stuff going on back then. Some here might enjoy seeing that.