Good shout, Philippe -- alas, this means that I need to rethink my 167 Stein in my Mühlhausen collection...I bought it and when it arrived it said "Kassel," so I was like "Oh well, at least the regiment is also in Mühlhausen," but now I know that two consonants switch places every so often in...
I see Weitze has a new GKR officer helmet for sale. I don't think it's this one because the enamel insignia (?) is different: https://www.weitze.com/militaria/33/Preussen_Helm_fuer_Offiziere_im_Regiment_Garde_du_Corps_bzw_Garde_Kuerassier_Regiment__492933.html
I collect around German regiments based in Mulhouse (Mülhausen) in Alsace, where my family is originally from. To my knowledge (feel free to correct me) those regiments are:
3 Badisches Dragoner-Regiment „Prinz Karl“ Nr. 22
Jäger Regiment zu Pferde No. 5
IR 112 and IR 167
Starting to move into...