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With 1.5" risers I'd go with +8". \\; My wife has a Deuce and I have a FX Springer. \\; The stock risers on both were about the same height (4.5"). \\; I put 12.5" chubbys on my Springer and used +6. \\; +8 will be more than enough - doubt it'll go too long.
I'm partial to doing my own wrenching so my vote is DIY. \\; Buy a service manual if you don't have one already. \\; It'll cost you a couple bucks but it's far less than dealer install and you'll have it forever. \\; Between the service manual and this site you should be ok.