You can write to Flower Hill or call them. They've always been very helpful to me and should be able to look up the plot information for you. If you go in person you can expect to find the cemetery in very good condition, although for some very old sections there may be no gravestones at all. I was there within the last 2 years.
Here's the info:
Flower Hill Cemetery
5433 Kennedy Blvd.
North Bergen NJ, 07047-3121 USA
Phone: (201) 867-0013