Here's how I mounted an Orion 9x50 right-angle finder scope on the rings of my LXD55 10" SN.
I used a flat steel bar, cut it to length, drilled it, and used hex-head cap screws into the existing tapped holes in the rings. I ordered the optional dovetail mount along with the scope and drilled 2 holes into the bar to mount it.
The finder goes on and off quickly and is held in place with the finger screw in the mount. The eyepiece swivels 180 degress for easy viewing from any position. The finder gives true right-side up images, and is a vast improvement over the Meade finder.
Jim