There were three ford 351 Cid engines for production. The 351 W(indsor), 351 C(levevland) and 351 M(odified??). I think the 351W came out in 1969 and the 351C in 1971 or 72. The 351M maybe in 76. don't quote me on those years. The 351R was a racing block for Nascar.
The 351W had 2V(barrel) and 4V heads in 69 and 70. The 4V heads were prized untill the after market sarted to make some heads. The 351W morfed into the 5.8, as the 302 morfed into the 5.0. So, you could get basically a 351W with fuel injection. Mainly in trucks, but I think the Mustang Cobra first year had a 5.8 in it.
The 351 C had a 2V head nad a 4V head. The 2V has streetable intake and exhuast ports, but open combustion chambers. They couldn't take to much compression ration, like 9:1. The 4v had large intake and exhuast ports. To much for the street, maybe even for racing. The 4v had closed combustion chambers. The Austrailian head ahd streetable ports and closed combustion chambers. The aussie heads and blocks were used in NASCAR in the late 70's to late 80's. the 351C had a smaller diameter crank journal (1.750), less drag. Also, used in the Pantera.
The 351M was a mutt, along with its sibling the 400M. It was used in Trucks and Full sized Broncos. It was a mixture of 351C and 351W specs. But I don't think much interchanged with the other engines. I think the bore spread was like the 351W, the heads like the 2V 351C with closed chamber and the front cover like the 351C.
The dirt track racers also mixed parts to make the 351 Clevor. Basically the 351W, with 351C heads and a custom intake manifold.
Tom