Dave go for a GT28RS, if you keep the boost below 12 psi you can get around without a tune for the time being. I would just do a run on the dyno to see what the AFR's are like though before you push it too much, but that'll only cost you $50. There is no point rebuilding the T28 when you will only get $4-500 when you go to sell it. you might as well put the rebuild money towards the GT28RS.
A 2871 is a bit to big to get around on without a tune, you would have to keep it below 9 psi and it would be dowie as and you wouldn't like it.