The photos are blurry, but bear with me. I finally pulled the trigger on a manual tran setup. Found a guy on Craigslist with a very tired 122 coupe who had spare M40, and an entire M40 setup in the car. We chatted a bit and came up with a fair price, and I came away with both transmissions, both bellhousings, the flywheel, pressure plate, clutch disc, a newer clutch master and slave, the pedal cluster (including accelerator), shifter, driveshaft, and trans crossmember ... plus a few other pieces. Came to $300 total, which seems like a good deal considering that by grabbing all the good bits from a single car I don't have to try and piece together it all from different and possibly incompatible parts.
Both transmissions look to be in fine shape, although the one in the car was indescribably filthy. The donor car had been stored in a leaky garage, with a floor covered in a thick layer of oil-soaked cat litter, for what looked like a century and a half. I've never seen so many spiders. It was very miserable to remove all the parts, but now it's done.
I'll try to take a bunch of photos and document how this goes, so hopefully I can answer questions for anyone else who tries this swap. The BW35 is coming out this week while I order a new clutch kit and bearings, and send the flywheel out to the shop to be resurfaced. And then it's modifying the crossmember, which shouldn't be too tough. More to come.