John G. Waite & Associates, an Albany, NY firm, does the sort of thing you are interested in persuing. They have done work for Thomas Jefferson's Monticello, Homewood (at Johns Hopkins University), Kenmore (in Fredericksburg, VA), the Peabody Essex Museum in Massachusetts and Tweed Courthouse in NYC. They have also tackled numerous private historic properties.
You can get an idea as to who is doing this sort of work already in your part of the country by contacting your State Historic Preservation office. In New Jersey the SHPO is under the Department of Environmental Protection. E-Mail inquiries to:
NJHPO@DEP.STATE.NJ.US