Here is a link on how to decipher a hull identification number (HIN):
http://www.boatsafe.com/nauticalknowhow/hin.htm
The first 3 digits of the HIN are the manufacturers code. XMR is the code for Ouachita Marine and Industrial Corp. They went out of business in 1980 according to the boating safety resource center:
http://www.uscgboating.org/recalls/mic_detail.aspx?id=XMR. From the rest of the code, I'm guessing the "1" is actually an "I", which would make your boat certified in April of 1975.
In terms of which model you have, I couldn't guess from the information above. Here is a link to a
fiberglassics page with information on some of the years and models. Post some pics and some users here may be able to help you.