A good refractometer costs about 8x what you'd spend to drain and refill, if you want to use test strips, your asking for trouble you don't need, just drain and refill.
A gallon of premix g-05 is 10 bucks a refractometer is at least 100 bucks for a crappy one.
If your just really interested in the coolant, take a sample and send it into Blackstone or similar.
I swapped to rotella elc at the 30k mark.
Factory fill should be 50/50 and with a -34f freezing point your boiling point depends on your pressure cap, assuming it's 16 psi, were talking 270f or so. (at sea level)
Basically it's so easy to dump and refill your coolant that simply saying the word coolant requires more work. Dump it every other oil change
.Using the drain at the bottom of the rad + a little 1/4 id hose and a 5 galln bucket, you'll get about 2 gallons out of it in 20 minutes or so. I've done this about 20 times during the process of switching to an elc coolant as i used a ton of de ionized water.
AFAIK Valvoline makes (zerex g-05) the factory fill of mopar and motorcraft gold coolant, it's just that mopar's coolant has a red dye.