If you go to
www.nhdeeds.com for Belknap county and go to Plan Drawer "L47" and Plan Number "9", you will see a survey of the land that was sold to the Catholic church. On it is reference to "Hidden Springs Road a/k/a Old Route 28" (confirming the earlier suspicion about the routing of Old 28). An older plan found at Plan Book 76 page 73 shows what the property looked like in 1974.