For me, after a few observations, logically and clearly a
98R, because of typical marking pattern usually seen on helmets of this regiment (not JR in front of the number but only R behind it).
Like this one:
Also note, that the bottom part of the "8" is much wider than the top part. On the number "9" this is exactly the opposite. The top part is bigger. Further, it is not a good idea to compare the "9" in the regiment mark with the other "9" in the company mark...Because those two marks were applied at different unit levels and at different time. The pattern of marking at those different levels was always different and it is mostly a very good sign auf authenticity to see those different patterms on the same helmet. First level: Bekleidungsamt, second level: unit Kammer, third level: Bataillon Kammer, fourth level: company Kammer.That´s the way to understand the different marks with their different typography.
The only other possibility
"could" be the JR99. But I don´t think so, because the JR99 pattern markings were not 99R but
JR99, just like this one

and most of the time, the BA XV is seen near the unit stamp)
Philippe
PS: Francois (festwagner), a helmet which would pleased you if it were in your collection, because garrison in Metz