OK, I've given it some thought here ....
If I went to the trouble of doing this, it'd have to be a top job! Therefore you'd have to use a Tremec 5 spd. Add to that a nice billet pedal assembly, change of axle, 3.55 in the rear and ofcourse the necessary clutch etc, add labour (the interior from dash outwards would have ot come out, gearbox alignment etc etc) ... would I be wrong in suggesting a healthy $15,000 - $20,000 ..... ?
All of a sudden that Turbo 400 ain't looking so bad .... ;-)