Help with fuel pump eccentric

If the cam is for a Magnum 318 and the timing chain is for a regular 318, it just won't work.
The Magnums were designed with fuel injection so a cam eccentric for a mechanical fuel pump was not needed. The snout would be shorter. I seem to recall reading something about having to change the whole front of the motor to accomodate a mechanical cam and that it would likely include the camshaft because of the snout.

Parts shouldn't be interchangable/mixed from what I can figure.