I recently converted a new Oscar Schidmt OGHS 1/2 size six string child's guitar to a four string tenor. I had bought the OGHS with hopes that it would be a inexpensive travel guitar. However, I could not get the low E string to sound right.
After talking with the Oscar Schidmt factory rep on the telephone who told me I would never get the low E string in tune or sound right, I decided to convert it to a tenor. Since the scale length was 22.5 inches, it was perfect for the changeover.
With a Dremel tool in hand I narrowed the width of the neck to 1 5/16 inches at the nut down to the 11th fret in a straight line with 1st and 6th pins holes. Not changing the original middle four pin positions at the bridge .
I made a new bone nut with an inch string spacing. With a set of J66's tuned to CGDA it sounds great. Even better with a capo at the second fret for Irish tunes tuned to DAEB.