When I swapped my 3-speed manual to a th350 in my 1971 4x4 (chassis), I did NOT have to change driveshafts.
What GM did with 67-72 trucks that came with a NP205 transfer case is put the transfer case mount in the same place on all trucks. The transmission length differences were made up in the transfer case adapter. Shorter transmissions got longer t-case adapters.
So if you are talking about a front shaft for a NP205, any 67-72 front shaft out of a NP205 t-case truck will work.
If you have something other than a NP205, I can't help.
If you don't know what a NP205 looks like click here:
http://67-72chevytrucks.com/vboard/s...d.php?t=266278