One other thought, sometimes the lip on the front CRT bracket means you have to lift the tube up a little before it will slide out, that might mean you have to loosen the Yoke mount to allow it to tilt up also. If the Yoke is hardwired to the chassis then this is pretty much what you are stuck with, if it plugs in via a socket you could unplug it and remove the whole thing together.
You really need an 8" Test CRT (8XP4) when working on a set like this so you don't have to keep installing and removing a big bulky CRT each time you want to test or tweak something.
See the bottom of this page:
http://antiqueradio.org/5AXP4PictureTube.htm
I would probably work on the chassis with the CRT in place, this has it's risks but it might be less risky in the long run than removing and installing that big jug many times.