'78 th350 / np203
'83 th350 / np208
Both should be 27 spline, correct?
In changing from a np203 to a np208, can I just swap the tailcone/t-case adapter from one TH350 to the other, or is the TH350 output shaft "stickout" length different?
Matt B

i stole this right off Off Road Design's webpage

the link:
http://www.offroaddesign.com/catalog/doubler.htm

A less popular auxillary method of attaching the NP203 to the TH350 is to use the TH350 with a longer output that was originally used with an NP208. You will use the 27 spline input in the NP203 to mate to this shaft and use the TH350 to NP208 adapter housing. This requires drilling and tapping new holes in the front of the NP203 to bolt it up in place of the NP208, and may require very minor machine work on the NP203 input bearing retainer. The drawback of the second technique mentioned here is that the factory TH350 to NP208 adapter housing is about 2.5" thick so your overall drivetrain length will be longer than using the factory 1" plate.

Thanks for that info Slotoy.
I wonder if I could get the NP208 to mate up to the np203 adapter? If I could, that would make for a shorter setup, but there probably is not enough meat on the 4 bolt adapter to get the 208 circular pattern drilled in it.
Matt B

Not gonna work. The shaft for the np203 is only 3/4" & the np208 version is around 5".
The in between the np208 & th350 there is a 1.5" spacer block & also the adapter.
Matt B