So the truck I just picked up has a 351m by the VIN number but the PO says "oh yeah it's a 351c". I know this couldn't be the case and it was not even a factor really anyways. I am tryin to research the components and I have found a Weber/Carter/Edelbrock 4bbl carb, an Edelbrock intake manifold for the 400, and aftermarket exhaust from the manifolds back. I was hoping for some help with identifying the cylinder heads without removing the valve covers. I am wondering what the significance of the stamp on the front of the drivers side head is . . . 5771. Probably not helpful, but this truck runs very strong and I am thinking there is a chance that one of the PO's rebuilt it as a 400. That would be cool as I eventually planned that anyways and it would save on component costs. Any help would be appreciated.
hey not much love here yeah? you could try checking the stoke down the plug hole to see if it is a 400. 4" is a 400, approx 3.5" is a 351M. Cant help with the heads, but old mate before you has done most of the good work on the intake and exhausts, so thats a good thing.
If they are Cleveland heads they will have "2" or "4" cast into the top left corner just outside the valve cover. Look at the drivers side head, easiest to see. I have seen a few heads with "M" in that spot, but most are just plain. If it is a Cleveland, the intake will be different from the "M" block motors. If you have a Performer 400 intake on there you have the "M" motor. As smiffy said, checking the stroke is the quickest way to tell if 351 or 400. Otherwise it's drop the pan & check the casting number on the crank. No fun there. If the PO installed a decent cam & straight up timing set when it was rebuilt you got a good one.