What was your father's name?
I have limited information on Shirks living in Mifflin Co. PA 1850 to 1952. They are connected by marriage to my Sulouff line. Reportedly, the Shirk surname was also spelled Schurch. I do not have the name Clarence Alvin Shirk b. 1890. Nearest birthdate in my records is for Andrew Shirk b. 1850, possibly your great-grandfather. He is shown in 1900 census as living in Armagh Twp, Mifflin Co., married 28 years, twelve children all still living. In that year seven of his children are named as still living at home, so presumably five of Andrew's children married and left home by 1900. I will be glad to give you all info I have and names of two other Shirk researchers who contacted me in 2003 & 2004. If interested please reply to this message board, furnishing the name of your father and a way to contact you.
As a suggestion, have you looked at the archived messages for Rootsweb's MailList for the surname Shirk?