Question on composition

[Mithlondor]

So, I have been with 35 mm for quite a while now, and I am perfectly aware of the rule of thirds, Fibonacci series and all those things associated with composition in a rectangle of "golden" proportions.

Now heres my question. I recently acquired a Pentax 67 (LOVE IT by the way). The one thing giving me fits at this point is composition in a non-golden rectangle. I realize I could just crop the living hell out of my pictures but thats really not what I am looking to do. Is there a similarly handy compostion guideline as the rule of thirds for near-square rectangles?

Any help is much appreciated

 

[motcon]

6x7, correct? the golden section/spiral/harmonics still apply, just scaled:

here it is with the harmonics: