The driveshaft used for 1969 Camaro w/Muncie 4-speed was 49.56" C-C on the U-joint trunnions. One of the several service part numbers was 3970521.
The production Z/28 driveshaft remains controversial. They are often seen with the trunnions aligned; for other Muncie applications they are offset as usual. The Assembly Manual does not list a part number. It is possible in production, Z/28s used a driveshaft balanced to a higher rpm.
For the record, 67-68 driveshafts are longer and used different trunnions. They don't interchange with '69s.