JDM von Weinberg , Jul 29, 2010; 05:55 p.m.
That's interesting, and a worthy project.
However, those who are construction-challenged might want to look at some of the commercially-made inverting eye-pieces that have been sold to convert various telephotos into spotting scopes. There are names of such units and pictures at (link).
The cost of either of the units I have was far less than $70, although they can be hard to find at eFence because the vendors don't know what to call them.