Cam and carb selections

Well, there you have it; the only thing NOT said was that you should get a 360!

I'm guessing you have made this trip already, with the 318;
so what was the result?
Are you towing anything?
Did you have to climb in second gear?
What speed were you able to maintain, in what gear, and how did you feel about that?
What trans and rear gear are you currently running?
Do you have alternates for either.
Are you expecting to make a lot of these trips?
I'm guessing, you were not happy, and are now looking for more power.

Why the Valiant and not a modern EFI-equipped car? They have automatic compensation for changes in elevation, for changes in air density, and so on.
I hesitate to say this, but,I don't see a cheap fix here.