Well David, it looks like they gave you all the right things to look for to determine if it's a 9in. The way you determine the splines is look at the end of the axle where your lugs are. The center area will be solid if it's 31 and it will be recessed in if it's a 28.
Welding the crack will work but I would replace it as soon as possible.
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69 351W Sportsroof deluxe
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