yeah about the stat amp an example you can find in the chapter 50-51 of the Manga when Incursio amplify the legs of Post-incursio training Tatsumi
and the head you can find when Tatsumi was fighting with the puppets of Kurome
and the head you can find when Tatsumi was fighting with the puppets of Kurome
Stat amp is covered by reactive evolution and the head part I wasn’t aware of