Would this be too much of a stretch?

Below is a bar/measure from an organ piece I'm composing. It's influenced by a form used by K.S. Sorabji, in which the almost all of the material throughout the movement is derived from a multitude of recurring thematic ideas. However, I am differing from the original form by not exposing all the material at once in an exposition, but gradually introducing more and more along the course of the movement.

At this point, there are three of the piece's recurring motives sounding at once, with occasional very slight alterations for harmonic purposes

(number 6 begins with a quotation of B-A-C-H, here transposed).

In order to make the presence of number 2 more noticeable, in the lower voice of the left hand, I considered that the accompanying quavers/eighth notes might be played on a separate manual (choir) with quieter registration, while the thematic material in the same hand is played on a louder one (great).

I'd like to ask any organists on YC, is it doable to play across 2 manuals with the same hand in this passage? Would only organists with freakishly large hands be able to do manage this? Not having access to a pipe organ with more than a single manual, I cannot check this myself.

Just tried it. It's not impossible. That is presuming Choir is below the Great manual. Good legato may not be possible in both lines.

If it were a French type organ with the G.O. on the bottom it gets tricky.

With my hand span I can reach a Maj 9 over the keys, and Maj 10 on the side of the keys.

Your span sounds similar to mine. Yes, it entirely relies on the choir manual being at the bottom for it to be playable. I assumed that most organs have that layout.

I considered the legato problem. I think it could be solved by "glissing" the notes with the thumb. A 1-2 1-2 etc. fingering on the choir would be ideal, but probably for large hands/very long fingers only. Thanks for the feedback!