This has been a question for everyone on here at one point or another. I don't think any of the options qualify as being "easy". I don't know what trans you currently have so I am going to assume it is a th350 auto, I'm also assuming your K5 is 4x4. In my opinion, the "easiest" thing to do is buy an nv4500 5 speed manual and convert the entire thing over to standard, but I am more comfortable with standards as opposed to autos. However, most people will say that the easiest thing to do is go with a 700r4 automatic. The main issue you get into is adapting this newer style transmission to your older style transfer case. In addition to costing more money, you also add length to you drive train because the newer tranny is longer. So you have to move you engine forward, move the transfer case back, or both...just depends on your preference. The FAQ section has a lot of good info, spend a few days in there and you will come out with a great deal more knowledge...and probably a couple more questions as well.
Start with these...
http://67-72chevytrucks.com/vboard/s...ad.php?t=33266
http://67-72chevytrucks.com/vboard/s...d.php?t=175504