[wheelbender6]

Tach installation is usually simple.
EBay post says "two internal leads.One is to be wrapped around a spark plug wire and the other is a ground wire".
Strip the end of one lead, wrap it around the plug wire and secure it with electrical tape.
The second lead can be wrapped around any bolt that screws into the frame for a ground. Loosen the bolt, wrap the lead around the bolt and re-tighten.
As for mounting the tach, you may be able to secure it to your handlebar fairing with zip ties. You could also make a mounting bracket out of an old license plate or something similar. Paint the bracket so it doesn't rust.
When I rode motorized bicycles, we had to make most of our brackets for mounting speedos, tachs, etc. It was part of the fun. I have used modified curtain rod brackets and other such common things.
You can do it.