the way to tell if the engine has heads on it is by pulling a plug and putting a dowel or similar down the hole and measure the stroke...I dont know what the strokes of the 3 are off the top of my head.
As for the 352 cast in the driver side front face of the block...thats there because ALL FE engines begin life as a 352 as far as bore goes...once they are all finish machined to whatever is required they become anything up to and including 428 engines...assuming its of course in the FE engine family...


- cs65