I have decided it's some version of a Homelite. Searching can't find any reference to this serial #. however for a start the oil filler port on the crankcase indicates it is 1964 or later. One big mystery is that there is no letter (A-F) under the 5 digit number cast into the block. Does te D13 on the attached plate provide a hint?  Any help would be reatly appreciated.