Is it okay to use mismatching tires?
Certain manufacturers sell different tires for front and back and I have run different tires on front and back on multiple bikes when one tire is worn or punctured and needed to be replaced, but the other tire still has tread/life.  Mixing brands isn't an issue other than one tire wearing faster than the other one.
It shouldn't matter which tire goes where, but judging at the rate that my tires wear, put the newer tire on the back since it will wear faster than the front tire. I usually move the older tire to the front since it will wear slower and if there are punctures caused by the age of the tire, it is easier to replace a front tire than a back..