I think it is around 84/85. Front der. braze on and aero crown start around 83/84. Columbus decals when SL/SP were the top of the heap did not indicate if they were SL or SP. If the bike was around 58cm CTT you would assume that it was SP. When SLX, TSX etc. started to be prevalent then Columbus started indicating the tubesets on the decals. This was after the mid 80's.

The # hanger would indicate a "team" bike.

What is the serial # on your Murray? I have an 86 tdf special with the Kl top tube.