I have a 1979 Ford F150. Original engine was a 351M. It kicked the bucket last year. Back in February, I purchased a 1978 Ford Bronco, supposedly with a rebuilt 400 engine and tranny with zero miles. I put the engine and tranny in my 79 F150. On the inaugural run, it didn't make it 10 miles, before what seemed like the oil pump went out on it and the rods started knocking. So, I pulled and disassembled the engine, ordered a new crank kit, and took the block and pistons to the machine shop. As I was disassembling the engine, I seen all the signs that the engine had been rebuilt. I could still see the marks on the cylinder walls left by the hone. When I removed the heads, the gaskets just fell right off. The pistons were brand new. But, as I was removing the pistons from the block, I was marking the side of the piston with a sharpie marker. After the second piston, I noticed the rod and caps had been stamped, either by the manufacturer, or the previous rebuilder. But, what I really noticed, was that the stamped numbers were from the opposite side of the block. The previous rebuilder had installed the pistons on the wrong sides, thus causing them to be backwards. When I went to pick up the pistons today, the machinest told me that that had happened just by him looking at the pistons (I didn't get to talk to him last week when I dropped the pistons off). He also asked if I had ordered the right crank, because the 351M and 400, are identical blocks. I said I just ordered one for a 400 because that is what I was told that it was. He checked the casting numbers for me, and sure enough, my 400 is really a 351M. I only paid $1000 for the Bronco, which had all knew body parts. I took the engine and tranny for myself, and parted out the rest. I got back more than I paid for it, but now I am rebuilding the rebuild. Can anyone tell me if there is any way of knowing what year the block is? Can it be deciphered by the casting number?

 

If it has the factory valve cover it should be on there

 

It had been rebuilt before I got it. The emissions label was gone. The valve covers were a little more square looking at the corners than the 351M originally in my truck. I don't know if there were a little difference in valve covers from one year to the next.

 

I got a 79 400 and it's valve covers are rounded

 

The valve covers on the 351M originally in my truck are rounded. The valve covers on the engine I'm working on now (considering they are the original valve covers) are also rounded, but, a little more sharply. The highest surface, where the oil fill cap is located, appears to be a little taller. Although I do not know what year the engine is, I do know that it is a 351M. I gathered that information from the crank cast number.