50/50 is fine.
If the system is empty I would add one bottle of antifreeze and then fill the rest of the system with distilled water until it is filled to capacity. You don't want or need 2 bottles of antifreeze unless in the coldest climates and the distilled water greatly slows corrosion of the cooling system. I have 128K on my Ranger with original thermostat and waterpump. The Radiator crapped out about 115K when the radiator seal started to drip. At that time I changed the upper and lower hoses and radiator cap. I still need to change my heater hoses and regret not doing that too. I would advise you change those out if the milage is over 100K on original hoses and the opportunity presents itself. Between 130 and 150K any original hoses are bound to fail. I have changed 3 ford radiators. 89LTD @ 90K, Ranger @ 115K and Explorer @ 100K. If you do a complete system overhaul with new thermostat and distilled water you will probably get 100K more out of the cooling system without incident if you change coolant at 50K. I am a firm believer in preventative maintenance. A few extra dollars spent now will save extra time and frustration later if you try to play out the life of each and every individual part. When I had my exploer radiator out I change a worn out tensioner, the thermostat and the serpentine belt in addition to all of the hoses because they were accessible and I knew I would be saving myself time and energy in the long run. rc