I tend to agree with David that this hilt can be classified as coteng; the small size also supports this notion. (Some Malay specialists consider coteng hilts a subgroup of tajong hilts - so, this may not necessarily exclude this hilt to be considered both...
However, the scabbard is not typical as already noted by you. While it does resemble a tajong scabbard, it does not exhibit the correct proportions - this may be due to its small size, craftsmanship issues, etc.
The hilt is paired with selut of horn.
This is most likely a repair since the base of these hilt cracks easily under mechanical stress.
The blade profile and the scabbard type are typically for a keris tajong I believe. You can make out a pale line the blade's forging.
There is no specific blade type with keris tajong. You probably have the pandai saras blade type in mind: While this type is very common, also other quality blades were traditionally utilized (carita, etc.).
Actually, this keris is not a pandai saras blade - it's a much simpler blade and of lesser craftsmanship. I've seen several examples of this variant blade and they seem to be of generally smaller size (none paired with any coteng nor tajong hilt!) and much simpler construction.
Coteng do even come with a greater diversity of blades than tajong hilts though...
Anyway, this is an interesting piece deserving further study - thanks for showing and David for bringing it back to the top!