Followup: I followed the youtube video method pretty closely. It was actually pretty easy after I managed to get the backbone off (next time I'll use a heavy knife or buy better kitchen shears). The 10 pounder just fit in my SM066. Since I had a quarter pound of butter under the skin of the breasts and thighs, I opted to use a 9 x 13 drip pan on a shelf under the turkey, with the pan lined with foil to extend its drip collection range.
The video example was 15 lbs at 275F for four hours. I allotted 3 1/2 hours with a possibility of 4. Well, the darned thing took just a bit over five hours to get the breast to 165, even though I boosted the temp to 300F (the limit of the SM066) at 4 hours. No real damage, just an unexpectedly late dinner. But, oh man, was it good. The breast meat was tender and juicy, the dark meat was perfect, and the smoke flavor was great (I used 2.5 oz of peach wood in three small chunks).
I am thinking that in using the drip pan the way I did, I really impacted the heat flow under the turkey. If I do this again (as I am being urged), I'll maybe just depend on the smoker's grease removal process, or maybe just a small pan to protect the top of the wood box to avoid any flare-up.
All-in-all, very satisfying result, even if frustrating ("Is it done yet??"). I'd read about smoked spatchcock turkey, but probably wouldn't have tried it without having watched the video.
Looking for bobmc's update!