I would suggest getting hold of a couple of level vials, or maybe a machinist's combination square with a head that can be rotated to a specific angle. Block the shaft or hold it in a vise (gently) so a vial on one U joint is level, then use the rotating level head to check the alignment of the other one. I assume the shaft is the open driveline type with a Cardan-type joint on both ends?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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