When I have installed the converter box with my analog TV, what sort of HD signal quality should I expect, assuming I have my antenna aimed properly. In other words, all things being equal, will the picture quality with this situation be just as good as if I had a true HD TV without the converter? How far from optimum antenna aiming can I be at and still get an acceptable HD picture? My antenna is a 25 year old Channel Master.
Michael, just to be clear, you cannot get HD on a non-HD television, no matter what kind of 'box' you may use with it. I assume the "converter box" you're referring to is the digital to analog box that will be necessary in order to enable old TVs to work when analog over the air TV signals go away less than a year from now. The signals from these boxes, however, will not be HD.
That's not to say you won't see some improvement in picture quality. Since the signals will be digital, there shouldn't be any problems (such as ghosting) common to analog broadcast signals.
BTW, your 25 yr. old antenna should work just fine.