To reduce optical problems like star distortions I had a local engineer make a 2" tube to fit the optics of the F/6.3 reducer inside and then slide that inside the draw tube.
What I had my engineer make is the same as what is sold here:
http://www.ziplink.net/users/lester/FLR.html
My problem was that I was trying to have a NGF-C crayford focuser in the mix:
SCT -> NGFC -> F/6.3 reducer -> meade spacer -> camera
... that didn't work well, there was distortion.
Having the reducer optics inside the focuser made all the difference. It also significantly shortened my imaging train so I can slew more south than I could otherwise.
I work at F/7.5. I can use the 3.3 optics to get f/5.5 ... but prefer 7.5.
Roger.