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If you have GIS you should be able to use the boundary file to get everything inside it and automagically calculated estimates for the split block groups or tracts. It's been too long since I have done it to explain it any better I'm afraid
I guess New England is fortunate in this respect....all of our census data is broken down by town and city, as well as the MSA's Tracts, and CDP's. The advantage of having no unincorporated places I guess.