If I were you I'd remove the paint using Andy's method, then re-measure. I would not turn the frame over to the LBS for facing without knowing what you're working with. Who knows what you might get back?
BTW- a really good source for fine cut files (used for chain sharpening) is your local chain saw shop. A flat file would be described as a depth guage file. Round files are available in sizes from 1/8' up to 1/4". These are good quality, and relatively cheap.