Dave,
Pre-war crt's are made from Pyrex and are very tough, but should be treated as any crt, with care. The best way to test them is in operation. You can of course at least check for a good getter and filament. These crt's use a 2.5V filament.
The crt is not actually loose in the set but is held in place inside the cardboard sleeve which is held by braces at the top. The rubber mask on top and wood escutcheon holds the crt down. If you do want to remove it, take the center wood escutcheon off (screws in the back and wing nuts towards the front), very carefully remove the socket and HV lead, and lift the crt AND cardboard sleeve straight up and out of the cabinet. You will be lifting the crt neck out through the yoke, so be careful not to put any undue side force on the neck. Just lift straight up.
You can see what the 12AP4 crt and cardboard sleeve look like here:
http://www.myvintagetv.com/picture_tubes.htm
Darryl