Which One Would You Use And Why !

[Mach1 Cobra Jet]

Ask me about a MOPAR and I can answer almost any question; but, I am new to the Ford scene. I am restoring my 69 Mach1. It was a 351W, long gone engine. I now have a choice of either using a 1970 351C or a 74 390. Which one can I get the most punch for the buck from and which would be the easiest and less expensive to swap into my Mustang. I would like to do a 428, but that has to wait for a while yet. I am looking at strickly street, but a good stong performer and often driven. I have a friend who knows Fords inside and out and has build some beautys and some very fast cars. He recommends the 351C. What do you think and I welcome any suggested modifications and any other ideas. Also would be interested in part sources. I am still looking for a Top Loader 4 Speed and a 3:50-1 center section for a 9" 28 spline rear. Would prefer posi-unit.

Thanks, David