The Overholt Cemetery you mention in Thorold is on private property. It is located on the old Overholt homestead and I am not sure who owns the property now. as for a transcription, I beleive there was one done about 10 years ago with the owners permission. The OGS has a copy for sale $1.75..
http://people.becon.org/~nbogs/publist.htm#thorold