Here are some pics that may help. I changed my truck from a 3 speed on the column to hydra-matic. I collected a complete hydra-matic rolling chassis and it was still an undertaking. I would not have it any other way now though. http://rides.webshots.com/album/327517089tVesKL

Maybe if you understand the reasons for some of the differences, it will make more sense. The frame is different so that the crossmembers bolt in so that trans can be removed from ubder the truck. Brake line routing is different fot the same reason. As Cletis mentioned, the firewall and trans cover are different so that access can be given to the bellhousing bolts from inside the cab. The starter is solenoid start instead of foot stomper so you get a neutral safety switch. Obviously linkage is different ( it is even different between same year GMC and Chevy trucks) and carb would have auto choke instead of manual choke. Tim already mentioned the driveshaft length difference. Hope this helps.