Guyon Morrison was born in Londonderry, NH as you stated in 1705. He died in June of 1783 in Chartiers Valley, Washington County, Pennsylvania. This information, and lot more is available through Geni.com, and MyHeritage.com. Also, you can get an electronic copy of "Biographical Record - Washington County, Pennsylvania. Biographical Sketches of Prominent and Representative Citizens" by Beers, and of many of the Early Settled Families." Start with page 658 for a complete picture of Guyon (Gavin) and his entire family through several generations.
Good luck tracking down the information you need. Let me know if this helps.
Felix (Fil) Morrison