" You couldn't take the parts (crank for example) out of it and put them in a 351 though. Stupid Ford."
That's because it wasn't a "small block". It got called a small block because you got one of the very early and rather desirable versions that had the smaller bellhousing pattern.
351M/400 blocks had an inch taller deck height and the cleveland bearing pattern (so actually, you could put the parts in a "small block", just not the windsors) and were really a "mid block". After 1972 they all had the bigger bellhousing pattern and were used as truck engines and intermediate selections for the big 70's cruisers.
Great motors, IF you were willing to change the cam. The emissions pattern cam from the 70's choked the everloving snot out of those engines, a low lift, medium overlap pattern that was installed a full 5 degrees from centerline... mix that with a restrictive intake (heads were just fine, flowed better than cleveland heads and almost as well as high-ports) that was only available as a 2 barrel, and you had a mix that made for a reputation as a boat anchor.
400M with stock heads, an aluminum 4 barrel intake, and even a mild "proper" camshaft installed centerline should be putting out at least 275 horsepower *easily*, out of the box even, if not more. All the emissions BS from the 70's had stock ones putting out, not a misprint here, 130 horsepower (albeit with almost 400lb-ft of torque just off idle).
Just keep the revs down below 6 grand, those massive crank journals also mean massive surface speed, real easy to break the hydraulic barrier and scuff 'em. I drove one of those motors with some mild mods for a while in a '79 Lincoln mark V... no idea on the power output but it was done with a larger Holley 2bbl and an RV cam, and was rather impressive. The nose of the car could rise on acceleration so far you couldn't see the road, even with a 2.47 rear end.
