The earliest model release were .27 engines as I recall and the later and more current are the .28 engines. Look at these links and you should be able to determine if one looks similar to yours.
.27 http://www.rufaster.com/87001.aspx
Hole to hole roughly 1 inch and 1/8

.28 http://www.rufaster.com/28PULLSTART.aspx
Hole to hole roughly 1 inch and 1/4

Hope this helps!