Another bad idea... volunteering... and not possessing the correct gear.

I've been ask to advise on a project to shoot an historic church for publication as a picture history of the church and the people.  As the conversation went on and the next thing I knew, I said I could do the shoot of the stained glass windows... oh right...  It's not that I don't know how, it is more that I am a stickler for the proper gear to do the job.  Yes, renting some... "why rent when you can buy?"  If this isn't a case of Gear-Acquisition-Syndrome...   So, top on my list is a 90mm 4x5 lens.  My Speedgraphic can do rise, but not tilts.  Shooting flat and off center from the plane of the subject means I should be good?  The trick is distance and distortion.  So the math is the angle degree from a 135mm X 50.8mm and / 2? X something = FOV + CA?  ... think I hurt my brain.