Delicious results provided you can live with the constraints.
The Zeiss CF lenses were all optimised (according to E Wildi) to have an image circle that encapsulated the 6x6 frame. So your 903 finder will show you that view.
But your sensor will rob you of some of it! the P45+ sensor size is 49.1 x 36.8 mm, so you're going to get a cropped image and you'd best use the ground glass finder and draw the dimensions onto it with a felt pen. Then add the back to save power. The shots will never look as expansive or elevated as they do in full 6x6, but still possess the incredible luminescence and sharpness the Biogon lens has in spades.
Next issue - I think it's CCD so power will be an issue. The battery does not last long esp since composing the shot to maximise usable content in the more limited frame will take an age. The CCD sensor needs tons more light than a CMOS but married to the Biogon, the images were heavenly. CMOS is more clinical and practical - CCD did possess a warmer, more artistic rendering of light. Softer, smudgier, more pastel like. Beautiful.
I think the P45 could do up to an hours exposure BUT only if your battery is up to it!
But you'll have an elegant and light setup - I had a 905 and I miss it. It was delightful. BTW the lens on the 903 is truly superior - it's more uniformly bright edge to edge.
And you'll need a camel - to haul all the batteries.
