Q:

Is there a screen alternative for a DSLR predating Live-View for photo review in the field? 

Is it possible to obtain something with a screen about postcard-sized that can either plug into my Canon EOS 20D camera and act as a larger screen, or alternatively will accept the CF card from the camera via a card reader, to check for focus accuracy.  I dont want to be carrying my laptop miles from the car. 

A:

Well, Canon 20D doesn't have live view and that makes it a little hard but I guess it shouldn't be that hard to hook a bigger monitor to it. 
I just looked up the B&H quickly and I found this portable monitor which has analog inputs:  
Vello RigVision 9" HD Camera Monitor
It has many different inputs and I guess you should be able to connect to your camera. 
You can find many other similar products with analog input here on B&H.
Also, because Epson P-3000 is discontinued, you can check other similar products, such as Sanho HyperDrive multimedia player and storage device.