slant daily driver buildup

I have a 1963 Dart that I want to build up for a daily driver. I have the motor that is in the car as well as a slant in a 73 duster. I believe both of them are 225's but I can not say for sure. What years do I want to look for with different parts to make a dependable motor for year round driving. I want to have decent power as I am driving 30 miles daily one way through the mountains and would like to still get as good of mileage as I can. Also what kind of mileage can I or should I expect?