They'll fit as they are the same size and profile. The "II" sight for the MLE is calibrated for Mk VI ammuntion, where as the LES 2 is for short rifles converted for Mk VII ammuntion. The LES III sight is for SMLE mk III and converted Mk IV rifles, using Mk VII ammunition. Pics attached below.
An MLE II sight will be incorrect for an SMLE, but beggars cant be choosers, and they'll do until you can find a correct LES marked sight.