UPPER DUBLIN In 1912, Richard V. Mattison transformed his Upper Dublin mansion into a castle, befitting a man who could be called a baron of industry.

Mattison, a pharmacist and founder of an Ambler company that was once a leading asbestos manufacturer, created what became a stone monument to the area's history and a backdrop in the 1966 movie The Trouble With Angels.

But decades later, the majestic structure once known as Lindenwold Castle and its 45 acres of rustic surroundings are slated to be sold to developers who want to build more than 350 houses marketed primarily to seniors and empty-nesters.

Neighbors and other residents are concerned about the potential change for their Montgomery County community and its most recognizable monument.

"We want to make sure our history is preserved," said Brett Pulli, whose great-grandfather emigrated from Italy and worked for Mattison as a stonemason.

Officials of the project developer, the Mattison Estate, say they plan to preserve the castle, two gatehouses, and parts of the formal gardens and lake on the property along Bethlehem Pike between Lindenwold and Highland Avenues. The development group is a joint venture of the Endeavor Property Group in Devon and two Blue Bell firms, Guidi Homes and the Goldenberg Group.

"We are not only developers of the site, but stewards of this site, and we take that responsibility seriously," said Brad Guidi of Guidi Homes.

The developers have a conditional agreement to buy the property from the Sisters of the Holy Family of Nazareth.

The Des Plaines, Ill., religious community, which operates Holy Family University in Northeast Philadelphia and Newtown, Bucks County, has owned the property since 1936.

The nuns formerly operated St. Mary's Villa for Children and Families on the estate for orphaned and abandoned children.

The religious community did not return calls seeking comment.

Guidi said the sisters had decided to sell the property because it no longer served their mission. The religious community leases the property to the Public Health Management Corp. of Philadelphia (PHMC) which runs a residence and day school for troubled youth called the Villa. About 70 youngsters live there and 10 attend its day program, said Diana Fryer, Villa executive director. The program, which serves youths ages 12 to 20, will continue no matter what happens with the Upper Dublin site.

The Mattison Estate's purchase is conditional upon a change in the property's zoning designation from institutional to residential.

The proposed development calls for 34 carriage houses, 54 townhouses, 40 condominiums, and 250 senior independent-living apartments. Prices could range from $300,000 to $750,000, the developers say.

No formal plans have yet been filed. If they are, the approval process could take 12 to 18 months before construction begins.

Last week, the developers discussed plans with neighbors in meetings at the Upper Dublin Township Building.

At the Tuesday meeting, neighbors asked questions about preservation issues, the density of the project, and potential increases in traffic.

Vanessa Anthony Klein, a member of a Facebook group called the Concerned Neighbors of the St. Mary's Villa, asked whether developers had considered building single-family houses, which would reduce the overall number of dwellings.

Peter Guidi of Guidi Homes said the proposed number of units was necessary for the project's economic viability.

The buildings on the estate are not protected by a government ordinance that would prevent demolition under any circumstance. But an effort is underway to include the parcel in a federal application to establish a national historic district in the area, said Mary Lou McFarland, a neighbor and senior preservation specialist with the Heritage Conservancy.

Including the property in the district would mean project plans could be reviewed by federal authorities, McFarland said.

The proposed district includes all properties affiliated with Mattison and his partner, Henry G. Keasbey, who built the Keasbey & Mattison Co. of Ambler into an asbestos powerhouse in the late 19th and early 20th centuries.

Mattison also built many of the community's landmarks with the help of his architect, Milton B. Bean of Lansdale, who designed the castle, the Ambler Gazette building, and eight stone mansions on Lindenwold Avenue Mattison had built for his executives, said Leopoldo Montoya, a retired librarian from Wyncote who has studied Bean's work.

In the 1960s, Bean's Lindenwold Castle was used in the filming of the movies The Trouble With Angels and its sequel, Where Angels Go, Trouble Follows, both starring Rosalind Russell as a nun coping with mischievous students.

Nearly five decades later, the Sisters of the Holy Family of Nazareth - who in real life mentored students at the site - may be cutting all ties, but many want the property's historic features to remain.

"You can't go back and buy your heritage," Pulli said. "Once it's gone. It's gone."