I have 2 682 runners. All the 671/681/682/2020 shells had the same part number inside, but depending on the year there are differences. 1948 and on had a hole for the e-unit. For the 682, a small boss with a hole was added for the extra linkage. The linkage attached to the boiler on the boss and pivots on it. The fakes will only have the push in hex head stud holding the linkage. It is a stud not a screw. (Many make the mistake of trying to unscrew it.)
One I have has been run a lot. The boss on one side has almost worn away.
Assembled you cant see the boss, you may see the "slop" in the action. If they were real good at fixing up an older casting, they put a small bushing in so there was no slop, but I don't think most were that good of fakes.