Drive shaft advice

[scimfish]

Hello all,
I am working on my '71 C20. I am changing the rear end out for a highway friendly gear ratio. I already have the rear end, it is from a '69 1/2 ton. Problem is, it's shorter than the old rear end, making my original 3/4 ton driveshaft too short. Does anyone have suggestions on what years/models I can pull a driveshaft from to make this up? Also, the original is a two piece driveshaft. I have researched specs and haven't had much luck so far. Any help would be appreciated.