They are for a couple of specific applications that I was comparing when I was researching the 60E to 80E swap in my red '97 (4.3L C1500), but now I'm starting to second guess how accurate that is as a blanket statement for '96+ trucks. Probably best to double check on RockAuto or one of the GM parts sites (Wholesale GM Parts Online, GM Parts Direct, Nemiga Parts, etc).
I don't recall my mechanic mentioning anything about adjusting the shift cable during my swap, but it's possible he did and never told me.
@Joe Dirte Question, does it act strange every time you shift into reverse or just the first time you get in and drive it for the day? The reason I ask is I have a similar issue after the 80E swap in my red truck. If it sits without being driven for a few days the torque converter will empty back into the trans, which makes the first gear selection take a few seconds because the pump has to engage and fill the converter with fluid again. At first I thought there was something wrong with the reverse in my junkyard 80E, but after a conversation with my mechanic and some testing I determined that it didn't matter which gear I selected, it happened in every one. Reverse was just the gear I happened to use first leaving the house every time. My solution is shifting to neutral for 3-5 seconds to get the pump going before grabbing a gear if the truck's been sitting for a few days, it works great.