my friend has a 2.8 with the 904. the 207 that was in it is blown up i have a np231 out from a 4.0 auto but the spline count is diffrent.

can i swap the input on the 23 spline 207 to the 21spline 231?

IIRC there were a few years when either the 231, 242, or both had 21 spline inputs, i think they were older, '87-91ish. what year is ur 231 from?

nope the 207 uses spur cut gears (straight cut) planetaries so they will not fit. however there are 23 spline 231s out there the only question is whether you need the short or the long one. that being said i do have both available maybe we can work somethin out.