With the swept back bars like the Wald and Nitto Albatross I have always just used the 100ish mm stem as a starting point and it was usually OK. In some cases it ends up coming back a cm or two, but that is generally for a customer that wants to be bolt upright, not any forward tilt to the torso. With the partial sweep like the Jitensha the stem usually comes back to an 80-90 unless you are striving for an aggressive position. Is sounds counter to that style of bar but some run them inverted, low and stretched out.