Everything you have said makes sense with what I've been looking to do. Here is a link 1950 Chevy 3100 w/C4
to a guy who's gone through a very similar widening of the front frame to install a C4 suspension... might be a help.
He mentioned the issues of matching the radiator support and fender mounting since the front was now wider... may be something to look into if you haven't considered this issue yet.
Do you plan on C-notching the rear to drop it down - or just install without much frame modification? I'd assume you'll naturally get a RAKE out of it without notching...
I was considering using an older 85-87 C4 setup to narrow the tread another inch ... but haven't pulled the trigger yet.