I'm installing some on a cantilevered-beam, flat roofed "ultramodern" house
from the 1950's. The original siding was similar to T-111 but the top layer
of fir veneer was smooth sanded. The stuff you get now has a rough-bandsawn
finish and looks a LOT buttuglier than the original did, besides not matching.
I smoothed the top layer using a minigrinder with 60 grit discs then
I did 3 sheets and then it was noon. I have never been covered with a thick
layer of wood dust even on the back of my jeans before. At the shop run
by the two brothers, brother #1 suggested cutting a sheet in half, running the
halves through their 42" sander, then biscuit joining the two halves back
together. Brother #2 said why not just dado some grooves in some 5/8"
ACX? If I can't find a source with smooth T111, which is unlikely, or anyplace
that has a 48" sander, brother #2's idea is the one that sounds best.