The pictures help. I'll agree it's an E. But, that looks like a brass round counter, which was used until 1981, after that they were steel. That flared grip is unusual! It, to me, looks factory, because of the rubber butt plate and the impressed checkering. Don't know any custom stock makers that would checker a stock like that on purpose! I'm sure there are lots of undocumented variations.
The other thing I noticed is the fore arm is wrong for an E. It should have a grooved fore arm, according to my reference book. But, when I look up 99E on line, it shows picture of a plain fore arm, with out a Schnabel.
Now I'm confused!