New Purchase: 1970 K10. Advice needed

[TheThirdPedal109]

I am the proud new owner of a bright red 1970 K-10 standard cab!
This was kind of a spur of the moment purchase (I chose it over an F100, which is a big deal for me)and I fully intend on making this baby a outdoorsy roadtrip-oriented vehicle.
Obviously I'm gonna have some questions since this is my first time venturing outside the Ford family.

Its got a 3 on the tree with the 350 upfront, no power breaks, no modifications with exception of the exhaust and its been well taken care of with complete maintenance records.

To start:

Any ideas on how to make this more fuel efficient? Carb spacers/EFI mods/different rear end/etc.

Yes, I know we buy classic trucks because they're special and the term "fuel efficiency" is relative, but my buddy and I are planning on going to California and back next-next summer(2017, we're from Georgia). As excited as we are to plan it, 8 mpg the whole time wouldn't be the most ideal setup for those 150 mile stretches without a gas station out West.

How much would it cost to install A/C and power brakes?

I hear Kansas gets really hot in the summer and the triangular window vents won't necessarily get the job done at 100 degrees, even doing 70. Plus day-to-day traffic would be pretty stressful without assisted braking.

What are some mods/customizations that you have found successful?

I see all these amazing cabs with great customizations and although I want to keep it simple; where does one to go find chrome trims, better looking seats, and upgraded dashes?

What are common problems associated with this second C/K generation that I should address?

I've already grown fond of this truck, especially since it's replacing a manual ranger with over 300,000 rough miles, so I intend on keeping it. Time isn't really an issue right now and I have two years to get these small projects completed.