This would work really nicely I think. I mean Duncan looks like he'd be willing to play with Gasol and maybe Duncan does a farewell tour? Some of the most under appreciated talent in Tim Duncan retiring makes me feel old

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If he's willing to come off the bench and take a 3 year deal with a P/O for say 18-24 million, this would be great as the Spurs would be the favourites to pull it off again next year. Re-sign Diaw, Mills and Baynes and bring him on and you'd have a potential lineup like this:
Parker/Mills/Joseph
Green/Belinelli
Leonard/Ginobili
Duncan/Diaw/Daye
Splitter/Gasol/Baynes
Plus #30 you could use on a Euro stash prospect and with Livio Jean-Charles still overseas developing, big things again and I think Duncan would be willing to entertain this even if they win the title.