Can I get some basic info on this engine?  I am looking at a 1969 Mach 1 with a 427.  Was this original equipment?  I intend to drive the vehicle often, not daily, what are your thoughts ?  

428 might be OE for that car, but not a 427.     You can find more info on Ford FE.Com.  That is the internet knowledge base for all FE type engines - 352, 390, 427, 428, etc.  If there really is a 427 in the car, then the motor at least is rare and quite valuable.  I'd be very, very skeptical that the engine was a real 427.