I did it. 180 t-stat.

Had knocking sound too, but did not replace anything. Knocking only flared up when engine temp broke 205f and higher. The highest the engine temp reached pre lower t-stat was 218. Since having installed the new 180 t-stat (2 weeks ago), 80% of my engine temp has been running high 180s, with an idle peak and cabin heat blowing , engine temp hit 196f. No more engine knock.

This past summer and before replacing t-stat, I ran 20-50 oil. Knocking occasionally flared up, but not as severely when I switched to Rotella t6 for the Boston winter. I'll keep the t6 in my Disco just to keep her insides clean.