Looking on line at summit at their Edelbrock cams....they do show different cams for the 351/400M and the 351C. the durations and lifts are completely different.

351C has significantly more lift and duration then what they show for the 351/400M. So it may be a matter of different profiles for those motors. The one you have seems to be a much more mild grind (Duration 282/292, Lift .484/.510 for the "M" as opposed to Duration 312/322, Lift .562/.588 for the "C")

So not sure it wouldn't work from a fit up stand point...

I think at this point...I would take it back and get what you know if for the cleveland engine.