Does anyone remember these old incandescent (rear projection) numerical displays of the 1960s or have any info on them?

Yup.  My dad had a clock radio that had one of those that was backlit by a blacklight fluorescent tube. 

Yup.  My dad had a clock radio that had one of those that was backlit by a blacklight fluorescent tube. 

Did it have LCDs to let light through in a controlled manner?

No.. it was more of reflecting purposes. 

The VOA/Marti transmitter plant in Greenville-both of them really used to use these displays on the antenna switcher that switched antennas to the transmitters.Above each transmitter was a larger backlit digital display.These went away in the later 90s to early 2000's when the antenna switcher system was upgraded to modern computer controlled-the relay room was upgraded to solid state switching.A computer in the control room with the antenna switching display on the monitor screen.Now its an Allen Bradly digital touchscreen display and controller.Do sort of miss those old incandescent digital displays.Remember changing bulbs in them.

No.. it was more of reflecting purposes. 

Did the display have an incandescent backlight?

It is backlight aswe see today with LCDs.
Each lamp has a figure stencil in front of it (one lamp has "1", second "2", and so on; it does not have to be numbers only, it could be anything), which is then projected onto the viewing screen (via the mirror). So once one lamp is lit, its symbol gets projected and so is displayed.
Funny enough, first time I've seen this concept was on a childs toy in the late 80's, showing different animal pictures on a small screen (there were 3 or 4 figures, all made of plastic, powered by few dry cells). Never thought this concept was ever seriously used as a numeric indicator display technology...

I do own such thing in my collection Just before Numerical LED display came out.  I  have one that
is rear Projected each segment of the Numerical readouts.  These Use a really interesting gold plated
 pin with a metal collar.  these slip into the metal block
 that been drilled out to have a common ground point
  and the gold pin part if lamp would slip into a socket
   they work like LED numerical display but these have
  5 volt and  about 50 mA filament per segment.

I do own such thing in my collection Just before Numerical LED display came out.  I  have one that
is rear Projected each segment of the Numerical readouts.  These Use a really interesting gold plated
 pin with a metal collar.  these slip into the metal block
 that been drilled out to have a common ground point
  and the gold pin part if lamp would slip into a socket
   they work like LED numerical display but these have
  5 volt and  about 50 mA filament per segment.

Can you post a picture of it here?

i would post it up when I can find it.   problem is it tucked
away deep in my mess.  as all my belonging is packed
up storage .  as  I am in the process building a home.
 I might have one loose in my light shed.