At the very end of GF I, there's a sign on the stone wall at the compound that says "5.6 acres for future commercial development and SOLD". Clemenza and Pentangeli both lived there, as is stated in GF II. Did the deal fall through or did Clemenza buy it?
If the sale was some kind of elaborate self dealing operation as has been suggested here, then it would make sense that the property was "sold" for commercial development. If for some reason commercial development could not take place (here the Corleones would have to fix a zoning board to rule against them),
then the commercial "buyer" would probably have had an escape clause in the contract. This would make the land much less valuable, which in turn would allow for a huge price reduction for Clemenza. My guess is that some Corleone owned entity continued to own the property because after Clemenza died it passed to Pentangeli, to there was probably some provision that the person running the New York operations could live there for life....which speaking of nit picking.....raises the question, what did they do with Clemenza's wife and kids? Put them on the street?