Q's about driveshaft??

[truckpower429]

Ok guys im just getting into the 67-72 chevys (GMC) but i have a 68 GMC with a 350 and a 3 speed manual tranny but im wanting to install a auto in it . but i was told by a buddy of mine that i have the drive shaft that has the larger type (or big block style) middle carrier bearing and i was wondering did all GMC's come with that type of driveshaft or was it optional? also would i be able to use a drive shaft out of a chevy with the control arms and springs instead of using one out of a leaf spring rear suspension truck ? thanks for any input .. Willie