The smaller stacks are the piston exhaust stacks, are they not?
That suggests that they'd "want" puffy bits of white smoke trailingthem.
Now, the boiler smoke probably ought to reflect a good strong wood fire. One burning to coals under the boilers. So, depending on how green-cut the boiler fuel was, the smoke could be a medium gray rather than sooty black.
Now, I'll wager those stacke built up in creosote and pitch, and may have flared at times--but probably not as a rule, given the length of those stacks.
Your kit, your choice is the bottom line, though.