Whether it's preban or not I can't say, but I can say this. It was NOT made in 1974 or 75. The only ARs Colt made in those years was marked "Model SP1" The term "Sporter" did not come into use until years later. The fact that someone went to the trouble to obscure the last digit, to try and create the impression that the gun was a mid '70s product does make me wonder tho.
Re the lack of safety stops; no Colt ARs ever had them. They are not needed on semi auto only rifles. The safety itself has only two positions, as determined by the way the safety itself is milled. Select fire ARs, and M16s, have safety/selectors that wil rotate 360 degrees if you don't have the stop shoulders on the lower. They are grooved all the way around. What I've wondered for years is, if Colt could figure out how to cut the 2 position safeties to stop themselves without and external shoulder, why the hell they didn't build the three postion safty selectors the same way and eliminate the need for those shoulders in the first place.
If Colt is now leaving those useless shoulders on their ARs, it's only because all the aftermarket makers do,so us civilians, who have no need for the things, will think it looks more like an M16; and looks sexier.[:D]
(Edited to add) The piece is apparently late preban, if the manufacturing list published on this site is accurate. Now I'm really wondering why somebody went to the trouble of blocking out the last digit?????