Mark Reinhart hit the nail on the head, that the Welte must be
regulated by ear. I will take that a step further and say that all
reproducers have to be. Yet most of them end with a gauge regulation.
But there is a better way than what you've read about.
When regulating a Duo-Art, for instance, the test roll is very
necessary to get you in range of the ballpark. From there, it takes
a number of rolls to get it perfect, and as the piano plays and the
valves settle tighter, it requires a little "touch" that it didn't need
beforehand. The regulator springs, which actually determine partly
the slope and partly the linearity of the expression box should actually
not be regulated too much at all, once the expression box has been
bench regulated under vacuum.
Regarding the Welte Licensee adjustment sequence, a test roll is a
requirement, but the procedure in the Welte Licensee book is clumsy and
will seldom get you a really good-playing instrument if you follow it.
I wrote a regulation procedure for the Welte Licensee and gave it to
PPCo. You should be able to order it or ask for it there. It is a
very good, reliable method of setting every instrument, and will turn
out exemplary pianos every time it is tried.
One very convenient feature of my method is that you are able to do
much of the initial regulation of a grand under vacuum while it is
still on its side, before it has to play the notes. So if the stack
has metal stem valves, this is a real plus, since Welte regulation
consists of endless back and forth adjustments. Each tweak of one
thing changes the other settings, which rely on stuffed air bleeds
and precise bellows positions.