Well, my mother now recalls that she was wrong.Although she does have an "uncle Thomas", we've identified him as from a different part of her family (not a Dow).My mother now thinks that Wallace, in addition to being an architect in the Dakotas, was the one who [partially] designed "Sing Sing Prison."
Unfortunately, the NY Dept. of Corrections page on Ossining Penn. doesn't identify the architect.
I think that this thread should be considered closed - we have sufficient leads to follow now.Thanks.