I'd go warmer than 60F for a gator. They can take those temps but would like it warmer.
Most of my big gators in the past were in ponds that would fluctuate with the ambient temperature with heaters to prevent it from dropping too cool. I usually set 65 as the minimum temp for the heaters.
Other similar sized gator gars were what had worked best for me. Aside from that I had good luck with niger catfish. Channel cats had worked with midsized gators.
Pims never seemed to do well. Their barbels would always disappear.
At one point I had a couple very large bowfin that got along well with the gators, though they squabbled with each other.