Looking at that diagram..
The thermistors form a simple (2.5V) voltage divider. So, you could use two
5k or two 10k etc. As long as they were nearly the same resistance
(when at the same temperature).
If they weren't the same, that
Adjust Pot can trim things out.
I think my old controller could easily be tweaked in using a small pot
on one of the input lines. (If it was indeed out of balance).