There are 3 machine heads which are the same and the D machine head is clearly different - it is an afterthought on the brass faceplate. I could well be wrong on this next bit, but the spacing of the original machines on both sides is also saying 3 stringer - wide apart on one side and the single one being in the center on the other side. I am entirely comfortable with my 3 stringer hypothesis which does put it into older bass territory. My 5 string has a new neck and the original was a 3 string to 4 string conversion.
Here is a 3 stringer I found - with guts as well (for the TONE!)