There is some interesting reading on the Chevelle forum if you want to go searching there. Here are a couple good threads on this subject.
can a slip on yoke from a th400 be used on a th400 that has a bolt on yoke
Turbo 400 Yoke Confusion
th400 bolt on yoke
On that last thread, pay particular attention to what jakeshoe says.
I got the measurements for my ds last night and will be calling Denny's today to order a Nitrous Ready ds. I will ask about the special slip yoke they have to replace the bolt on yoke.