Roy, I've got it. Unfortunately the sides of the receiver were cut away along with the original serial number if there was one. It does have what I take to be a serial number. It's starts with an S followed by a four digit number stamped on the receiver. The serial number is covered up when the stock is on the rifle.
here are a couple of pics.
It will be covered in my new book. In excruciating detail of course.
It is based on a 99C. they were introduced in 1965 and we have seen 284's produced in 1964 (DL's and F's with hand checkering) so this can't be the earliest one.