Losing Coolant

[Kisner]

The motor is newly rebuilt (less than 100 miles on it), however, it sat up (cranked every weekend though) for about 8 years during the restoration process. There's no foam in the coolant, no water in the oil, and no other leaks anywhere else. Water pump appears (on the outside) to be working perfectly and engine runs great. All hoses and clamps are new and seated perfectly. One thing I may have screwed up though is that I believe I'm running 70% anti-freeze and 30% water. I also had it filled to the top of the radiator - didn't think to allow room for expansion. If I have too much anti-freeze will that make it expand out the overflow tube?