driveshaft options

[Liltroy]

Ok Im putting a LQ4/4L80e into my 74 stepside shirt bed. I'm using 1" motor mount adapters. truck had a TH375 in it(TH400 with a long tail that uses a TH350 slip yoke). I know I'm at least going to have to change yokes but my question is should I get the driveshaft out of the silverado 2500hd that the transmission came out of or try to have a new yoke on my driveshaft? I'm pretty sure I'm going to need a longer driveshaft than what I have but not sure of exact measurements yet. I just wanna know which driveshaft I should work with because I may get a deal on the driveshaft when I go to get the trans next week if I get them together. Any help would be greatly appreciated.