Hi, Brian. I'm not sure I understand what you are trying to do. Are the plaster keys gone so you have big "bubbles" on your walls and ceilings? If this is the case, they usually just put the drywall over the old plaster--if they can find the studs.
In old houses, it is normal to find stud spacing much different than what we use today. In a 150 year old house I know well, the 2x4 studs (full dimension) have the wide side facing the wall instead of the narrow side of the 2x4. And the spacing is "sort of" on 16 inch centers. Been that way for a long time, though. And it is impossible to find the studs with a "stud finder" because of the lath and nails. This is just to let you know about some of the things you might find, and this house has drywall over the lath and plaster in most of the rooms. Drywall screws will not hold in just the lath. They have to be into a stud.
This might answer some questions so please let us know more about your problem if it doesn't.