Since you just purchased a used unit, the first step is to do a factory reset (MENU 0999, or in the Save Menu). Then do a Save (Menu up-arrow OK OK OK) to make the default settings permanent. Use output for audio to your receiver, and output for video to the display.
With a 2.35 (or even a 2.4) screen I would suggest you select 2.35 as the output aspect ratio in the Output Style menu for the selected output configuration. If you have the lens on a sled so you need both 16:9 and 2.35, then you would need to use the "Output per input aspect" option in that menu.
We have a number of Tech Tips you should read to help you understand setting up the Radiance. These are at http://www.lumagen.com/testindex.php?module=manuals
. TechTip 3, 7, and 16 all have information on setting up a projection system with an anamorphic lens. Remember that after any changes, if you want those changes to be permanent you need to do a Save.
For SD letter box material, such as is on a laser-disc, you select the input aspect as LBOX. This is specifically for 16:9 source in letter box format. When you press LBOX, if the source is a 16:9 letter box source format, you would fill the height (if the output aspect is 2.35). For a 2.35 letter box source, you would also need to zoom in using the up-arrow, so the 2.35 letter box source fills the screen.
One other note on SD 2.35 letterbox: The source material for 2.35 letter-box has only 272 lines of active source, and on laser disc, this is generally interlace source. SD interlace can be film source such as is on many DVDs, but historically I found that the laser discs I looked at (other than a few CAV discs) were not progressive with pull-down, but true interlace. This further reduces the vertical resolution. So for interlaced laser discs the true vertical resolution is less than half that of a "film encoded" DVD even if that DVD is encoded on the disc as interlace. This along with the limitation of the laser disc format will limit the quality of the up-sampled image. You can improve the image using the noise reduction and edge enhancement features in the Radiance input menu.