You don't need to increase the size of the head sides. All you need to do is to cut the gusset pattern in half lengthwise from nose to back of neck, and then be sure to add standard seam allowances to each side of the gusset, including the edges you've cut.
Basically, the center-seamed head was developed by Steiff only to economize on mohair. By cutting out every 8th (or 9th?) gusset in two parts, they minimized waste. The center seam was not used for extra shaping.
However, since they were produced in smaller quantities, these center-seamed bears are relatively rare, and have a definite charm of their own!
While I'm drawing and uploading, here is a link that might help. http://www.teddy-talk.com/viewtopic.php … 27#p267027