as i understand it the fresnel is clipped to the dowel and the dowel is hung from the top of the box... the main issue i see with this method is is drastically alters the central focal point of the fresnel being corrected, it does this in 2 ways:
1) the central focal point is lifted, however slighlty taking it out of aligment with the rest of the assembly. I might be possible to correct this by simply spacing the fresnel out from the dowel... ?
2) the bottom of the fresnel is drastically lifted above its properly aligned possition in the assembly... this could be somewhat corrected using the above mentioned method...
3) # 1 and 2 greatly limit the assembly's ability to correct keystoning...