Red is 100 %. You'll mix with distilled water 50/50. So 2 gal of red yields 4 gallon of system coolant. 100 series with rear heaters take 4 gallons.
Just changing radiator. Without a full flush, draining of block drains and blowing out heater cores. 1 gallon of red may due.
I strongly recommend flushing the coolant system in the 98-02 with distilled water, 3 times, before remove old radiator. Replace rad cap, thermostat also heater Tees if not done.
If I've any concerns with contaminated or deposit in the system. I use a chemical flush "BG Cooling system cleaner & supper cool pack", before first drain.