If it were me, I would have an adapter machined similar to the earlier post with the flange mounted u-joint. Then you won't have to monkey around with a weird custom driveshaft that no one wants to touch, not to mention the possible vibration problems of mixing a u-joint with a flex disk.

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For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel