Drill holes and use bolts with Nylocks. You might have to take it apart sometime.
You also might watch to see, on a 60° plus joint, how much slack you need for it to work back and forth on the shaft. Don't bolt or weld one end of the shaft so that it can move laterally if need be . . Anytime you're over 45° with a U-Joint there's a natural tendency to bind, so don't booby trap it . .
Also, on your intermediate shaft, support it with a bearing or two. (depending upon length of run) You can use Hiem Joints as "rabbit" showed or other types, but you will need something to keep the intermediate shaft from flopping or creating a bind at the sharpest degree joint.