For IGFA legal leaders, your shock cannot exceed 12" including the knots. The class tippet must be 15" NOT including the knots. I use 80lb Ande's for the butt section, 10kg Rio IGFA Hard for the class tippet, and now use 80lb FC for the shock as it seems to be more abrasion resistant. I use Trey's method of attaching a strong braided loop to the flyline. I use a perfection loop at both ends of the butt. I then use a bimini with the double line surgeon's to loop onto that perfection. I do not use a bimini on the other end of the class. Using Stu Apte's improved blood knot doesn't require it and therefore makes for a smoother connection. That knot is in Trey's book. Recently I've been practicing tying the slim beauty knot for that same purpose. I hope to have faith in it before I head to Guatemala next February. That knot does not require a bimini either so both that and the Stu Apte knot are slimmer than a huffnagel. I find the non-slip loop takes up too much shock material and find no advantage to having a free swinging fly for billfishing. Therefore I use the ancient 3 1/2 turn clinch knot and cinch it down real tightly using a commercial knot lubricant. I've never had one fail. If I break it is almost always just above (toward the flyline) the class/shock connection.
For non-legal, I would do everything the same, but as mentioned earlier I would increase the length of the shock to about 3ft. I would not exceed 10kg for my class tippet for safety reasons.