Place insulation in front of drywall?

I have a 1972 constructed home it is constructed of block the exterior drywall it is separated from the block by furring strips which creates an air space of about 1" .This does not allow me enough space to get any insulation behind the wall foam or otherwise.I do not want to pull the sheetrock off for obvious cost and labor.Can I add ridgid foam to the outside of the drywall ande cover with gypsum? If yes any hints on type of ridgid foam.Also can I add foam around the foundation to insulate the concrete.Thanks Mike