I'm a self admiitted Admiral junkie :P
1. As stated above the contrast affects the gain / AGC, so what you observe is normal.
2. About 1/2". Here's a photo of a freshly pulled chassis with tape measure. Also be sure your yoke is snuggly against the CRT bell and that the dual ion trap magnet is on the right way. The blue section goes towards the CRT face.
3. Could be related to #2. Also, have you adjusted the Hor. Lock and Hor. Drive as described in the service info ?
4. Yes, these early Admiral do have prominent retrace lines, but they are excessive in your photo I think. You should be able to adjust the brightness and contrast and get a picture like this taken from a similar Admiral set. What are you using for a video source ? I'm using an over the air DTV receiver through a 75-300 ohm balun to the antenna terminals.
