If you set up your second ring and pinion (correct shims, etc.) and use a solid bearing spacer (no crush sleeve), you can change the 12 bolt as fast as you can change the 9". And it will be cheaper to build the 12 bolt. The major downside I can see for your situation is that you are going to run a 283 and the ratios you will need (6.00+) are much stronger in the 9" or a Dana than in a 12 bolt.
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