Tim,
I just read about your difficulty in cold-bending your new tiller lamination, and your consideration of a steam box.
My (unsolicited) advice: don't go overboard. Steam is steam.
I've worked with some really slick steam box setups that use huge propane-fired kettles, have stickers for the wood to rest on to assure good steam exposure, gasketed doors, etc. They work really well.
Know what else works well? A $12 hotpot and a length of 6" pvc pipe.
Set the hotpot on the ground, rest one end of the pipe on the spout of the hotpot (so condensation drips back into the pot), and secure the other end in your bench vise. Stuff a lump of rag in the top end of the pipe, wrap a wet rag around the bottom end/steam spout. Steam away.
I later refined this contraption by adding a pair of small screws near the upper end of the pipe so I could tether shorter pieces of wood to prevent them sliding all the way down the pipe, and by draping a blanket over the pipe to retain more heat when I was cooking a nice fat 2x2 piece of oak.
I find that the hardest thing is to resist the urge to make wooden pretzels.