its not too hard most the differences in the forks between 750 models was how everything else ie brake calipers and things bolted on. All you need to make sure of is the length the same and the diameter the same.
thanks for reply.photos look same for mounts.dealer thinks tubes may be +2.I also have triple tree from 80 750 K there in really good shape but wouldn't fit my 81 custom.anyone interested?