I had a '78 F150 with a 400M, 9" rear and DANA 44 front and a C6 (NP205 transfer case) and man that thing was indestructable. Great torque for a small block. That block is given a bad wrap because it has the same oiling problems as the regular cleveland engines and because of the smog police, it's ladened with smog stuff and restrictive intake/exhaust and i think it's also a siamese bore block (no cooling passages between bores, but i'm not absolutely sure on that). The large stroke in that engine is great for producing lots of lowend torque and you really don't need to even touch the heads except for maybe the valve springs because of the large stock intake and exhaust valves as well as good sized ports. The 400M is a horrible drag race engine (hates high rpm's because of the increased piston speed from the stroke), but for low rpm torque and for idling along offroad trails it's a great engine. The good thing about the 400M is that it has the big block bellhousing pattern so you can put the better 460 engine in it's place. The 460 is a better engine in almost every respect, but i still have a soft spot for the clevelands.
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'84 Mustang 5.0 LX
My car