I really do not know what to think about this Tschako... The chinstrap is not original!
The markings are very old for this pattern, dated 1866 and regimentally marked with IB, 3. Thüringisches-Infanterie-Regiment. Formed on May 5, 1860, as the 31st Combined Infantry Regiment from the three Landwehr core battalions: Erfurt (1st Battalion), Mühlhausen (2nd Battalion), and Sangerhausen (Fusilier Battalion) of the 31st Landwehr Regiment.
This old initial Landwehr formation of the regiment is maybe the explanation that we have here a Tschako marked with this thurigian unit, as this unit normally wore the Pickelhaube.
But this Wappen is not born on this Tschako, as the M91 side posts, the Wappen and the iron grommets...
Philippe