I'm afraid that picture is actually no help at all. The reason why your bike does not match either model exactly is because the picture shows the 1980 L and E models; you have a 1981, and neither the L nor the E model were produced for 1981. The E and L versions were discontinued in 1980, and for 1981 the two choices were the G and the GL. Both had the round headlight, but the G model had the tail from the old E model. From what you describe, you have a 1981 GS750 G and you should be looking for parts for that, and not for the 1980 and earlier GS750 L or E.