I know for a fact the W is easer. The 400 is not a bad fit in fact the 400 fits better than the 351C because the heads are an inch taller on the block and it gives more room for the headers. The W is a stock deal everything about it is easer to make happen. I just like the C motors and I wanted EFI so here I am. It's not that hard, if it was I couldn't do it. I am no super mechanic by any means, I am a carpenter. Do what you want, enjoy. Life is short.
Bax