I don't think welding will work.
The ring gear is steel and the fly wheel is cast iron.
Get a used fly wheel and have it balanced against the old one.
Or just install the (new) used one and hope for the best.

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76 240 D. Bought in 1998 for $25.
85 300D. Got it for free with a bad engine. ( Sold )
60 Unimog 404. What was left of it, was given to me. Now powerd by 617A.
88 560 SEL. Bought without engine and trans. Now powerd by 617A.
67 250 SE. Cuope. For resto or sale.
64 220SE. For resto.