First off, welcome to this great site from another FXR owner!

Hard to see from the pic, but I don't see the caliper mounting boss on the right fork leg for a second caliper. A dual disc arrangement requires a master with a bore for dual discs, a single brakline from it to a tee splitting off to both calipers, bosses on both fork legs, and a wheel with dual hubs to mount both rotors. I doubt he modified all that. It's not unusual for HD to change design mid-model year. I'm not an expert on what came with what, but it doesn't appear that bike was setup for dual front brakes. The PO went thru a lot of trouble to remove any semblance of dual front brakes if he changed it out. Chances are it never had them. 
Enjoy your new ride and this great site!!! 
Hoist! 
Added:
Yours seem to have a taller front suspension. I'll let the FXR history buffs try this. There were might have been some different FXR '86 Liberty Edition Models that had different setups, is one guess.
The second one appears to have had the front end apart and modified. Note the reflector bosses taken out of them. They're smooth. While they were apart, he could've added the second brake setup then. And a big ole rear suspension. That bike's been modifed some. So no standard dual disc is my other guess! 
Great catch on the aftermarket lower legs on the first comparison bike I posted. On page 287 of "The Big Book Of Harley-Davidson" by Tom Bolfort, Rich Teerlink is seated on a Liberty FXR with Vaughn Beals over his shoulder reading the ticker tape in the American Stock Exchange. On this bike, it has laced wheels and is a single disc front end. Also, reading the orginal author's information posted in this thread, it sounds as if the Liberty was based on the lower trim level FXRS. I think it may have also had the higher suspension, I need to re-read the original post to figure that out.
The history of my bike is pretty simple. It was part of C & C Harley-Davidson's (Tulsa, Ok. now Rte. 66 H-D) 1986 allotment. The story as I have is it was stolen from C & C by a fellow who came in to test ride it. Somehow, it was located in Arkansas a year later. Once it was recovered, one of the mechanics bought the bike and kept it till last year. Apparently, he fell on hard times, used the bike to collateralize a loan with his credit union and it got repo'd. I "knewish" the guy about 7-8 years ago, but have no idea where he is today. I've also known the previous owner of C & C and am going to try and get ahold of him to see if he might still have any of the original documentation from when the bike was ordered or any of the series documents (i.e. bike # of 744 built).
I also trolled the internet this afternoon and found more for sale ads for comparison photos. A random sampling shows an "all original" with a Fat Boy front end and fender, another with the cast wheels, and one which was painted in a Pink Floyd theme.
To better understand why I'm a little nutty about "originality" on this bike is there were only 744 made. Doesn't necessarily make it worth vastly more than other FXR's of the day right now, but then again, who ever thought a 1971 Superglide would be worth more with the boat tail, or the '77 XLCR cafe racer or '83 XR-1000 would ever be highly sought-after collectibles?

Other obvious items on this I've figured out is it should be an "all-blonde" engine. The jugs and rocker boxes have been painted black and it's got the Ness-Tech plastic side covers.
In addition to a Heritage Softail, I've owned a (in no particular order) 1965 Electra-Glide, 1957 FLH, 1945 UL police bike, 1945 EL Knucklehead, several 1942 WLA's, three 1942 XA shaft drives, 1965 Servicar, 1957 XLA military issue Sportster, and a number of Hummer and Aeromacci varients, and many different bikes that I flipped too quick to remember. I've got a 1948 125cc Hummer and a 1962 XLCH Sportster project. So, I do get wrapped up in the originality aspect or "period custom" aspect of older Harleys.
I have a lot of respect for Alan Girdler and Greg Field and their research, but their work is not infallible, nor the final word. Especially when some Harley model years were rolling prototypes.
I'm going to keep an eye out for a very good deal on an FXR 2, 3, or 4. I'm hooked on this chassis now. Here's another with cast wheels: