Doug
The mirror is vital..it must be a front surface mirror. An ordinary mirror will give you double images-just unworkable.If the mirror is not good quality you will soon experience severe discomfort when observing, so it is very important to get this right
The exact distance to mirror from the bino objectives doesnt seem to be a critical parameter-within reason.
It is usual to design your mount so that the binos are at 55 deg angle-I built mine to allow two angles-45 deg and 55 deg and in practice use the 45 deg as it is more comfortable
Remember that if you allow the mirror to rotate enough you can actually use the mount to view objects that are behind you in the sky as well as objects from horizon to zenith, so you dont need to swivel around as often
here's some other approachs to building a mirror mount
http://www.stargazing.com/bino/
http://www.indytel.com/~rnabholz/downbino/
http://mywebpages.comcast.net/observ...cularmount.htm
Narayan