I have follow Pola housing and try to find a wide angle lens for this. Wider is better.
I ask for tthe 65 becauce i found a extremly inexpensive one but i take a look to the 8/65
If you just need to borrow one I can lend you mine.
If you don't need anything that wide the Angulon 90/6.8 might be of interest.
They are cheap and abundant.
(Känns lite dumt att skriva på engelska till en annan svensk).
Remember that when stopping down you get more coverage, so I think you'll be fine at f32 at infinity. If you are going closer than infinity you'll also get better coverage, so f22 or maybe even f16 will get you enough coverage. The Polaroid Tominon 75 mm lens will cover, but that's less wide angle...
At least it covers the exposed area of 8.5 x 7.3cm for the polaroid back for the Super Technika 6x9 quite well. See the example in:
(there was a url link here which no longer exists)
I was thinking to set it at hyperfocal distance, if i can calculate it correct and later add a finder. Mostly i like to build a simple cary on WA landscape polaroid camera as the ones i have as 250 and 180 are not wide enough
A 65mm lens on a 65 x 90mm format is roughly the same as a 30mm lens on 35mm film. You may be able to find a wide angle single use camera from which the viewfinder can be easily removed which will show a similar field of view.