i have a 78 sportster that i wish to convert if cost effective to disc rear brake.I have purchased a powdercoated rim the i believe is off a softtail aroud 2000 so i would need to put a disc on the left hand side and calliper to suit and a new cog for the right.Is there anyone who does this sort of thing in a kit form?

 not these days , you would have too modify too suit, 1979 sporty is the 1st production model with the rear disc brake in 79 up the frames are different