A friend of mine and avid collector has had an L1A1 for years. Here in the Socialist Republik Kanada since it's registered (all restricted class {handguns ar's etc. } and prohibited [FN's, full auto stuff] has been for years, this happened before the long gun registration fiasco) FN-FALs here are roughly the equivilent to class3, it's about as much as you can get, and there is no difference between a select fire FN and a semi- same classification, stupid but true. Anyway, apparently the only difference between semi and select fire selectors is that the semi ones are longer so that semi-auto position is as far down as the selector can travel due to the fact that it's longer at the front than auto ones, and hits the upper. I heard an old soldiers trick years ago, apparently when it was decided that the FNs were uncontrolable in auto the armorers fitted the guns with the longer levers (that came in contact with the upper when in semi, thus preventing them rotating to auto). What the troops used to do was break the action open so that the upper was out of the way, and then rotate it to the auto position and close again. Of course you had to break it open again to get it back, and if the Sgt-Major caught you you were toast. My frien has had this gun for years, and I tried it (empty of course!) I broke the action and rotated it. There were no "auto" markings on the receiver, but there was a indentation in the receiver for the detent ball to grab (same size and shap as the indent for semi- mode) I then closed the action and proceded to work the bolt handle. You guessed it, every time the bolt went fully ahead the hammer went "click!" My friend had never known, and since it didn't affect the status of the weapon he ground down the offending flange on the selector until it just cleared the upper while on it's way to auto. He was pretty happy, although that's more than I can say for his son, since the rifle is registered it's has to be destroyed after the owner dies, no if ands or buts! It can't even be de-milled into a wall-hanger or a momento to be passed on to his son, the day he dies (assuming the records haven't been lost, which is likely with our system) the police confiscate it.
Just thought it was interesting, since AR semi-only selectors won't allow full auto even if all the other parts are there, but an L1A1 selector is the same except for the larger flange that stops it from rotating to auto.