The weak link is the center cardon joint-an early CV joint arrangement with 2 u-joints and a spring loaded centering ball and socket. If that centering ball and socket are worn/broken you cannot get the vibration out of the driveshaft.
The quick check is that if the joint snaps over center it’s “good” for now. If it just flops around it’s not functioning for one of several reasons with that centering ball/socket joint. One of the problems is the ball in the joint is not replaceable, The rebuild kits that are NLA new had a new yoke with the ball that all got replaced. Who know’s how long an old good one will last. Lots of them are being run right now, some of which are no good. Test yours and if it’s bad try to find a good DS or less likely a rebuild kit.
I had a new shaft made locally with modern parts as I needed to shorten it anyway for my trans update. Very stout, modern parts, not cheap. There is also a company in TX that rebuilds the orig DS with a new machined in ball and socket using parts that are available-about $1000 as I recall.
There is a whole discussion in the forum on this but I can’t find it without the old search feature-maybe someone else can.