Your flathead can be dependable and give you many trouble free miles. Convert it to 12 volts and make sure a professional rebuilds it.
Your drivetain can easily be changed over to the highway traveling by using a lowered front axle (very good handling) and a 40's style ford car transmission and rear end. Most of these are a simple bolt in on your ford. This will give you the highway gears you need. My opinion, these components will make it more consistant to the year the ford is and still be reliable.