I just thought I would post a link to this topic:
http://www.dotheton.com/forum/index.php?topic=7401.0
As the construction of your rearsets seems very similar, for anyone else who might be wondering the details of how they are constructed. Maybe you could show pictures of how you went about making yours and/or any progress pictures? In the link I posted, the OP talked of enlarging the hole and using loctite, maybe he could post how they lasted or any shortcomings (If he is still around, thread was from 2009).
Nice work, though, and probably a better call taking them to the machine shop.