Lucky the multi-measurement Pom caught it
The optical diameter of the reducer is only 52mm camera side IIRC so 3" is probably overkill, but then 2" would be too narrow for your sensor.
FWIW, the only time I've tried DSO imaging with mine, the seeing has been sufficiently poor to destroy any resolution advantage of the focal length. If you consistently get better seeing, then let me know how you get on!